| Message ID | 20231129-riscv-restrict-dwarf5-llvm-v1-2-ec0d368fb538@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | RISC-V: Disable DWARF5 with known broken LLVM versions | expand |
On Wed, Nov 29, 2023 at 3:30 PM Nathan Chancellor <nathan@kernel.org> wrote: > > LLVM prior to 18.0.0 would generate incorrect debug info for DWARF5 due > to linker relaxation, which was worked around in clang by defaulting > RISC-V to DWARF4 [1]. Unfortunately, this workaround does not work for > the kernel because the DWARF version can be independently changed from > the default in Kconfig. > > Do not allow DWARF5 to be selected for RISC-V when using linker > relaxation (ld.lld >= 15.0.0) and a version of LLVM that does not have > the fixes (the integrated assembler [2] and ld.lld [3] < 18.0.0) > necessary to generate the correct debug info. > > Link: https://github.com/llvm/llvm-project/commit/bbc0f99f3bc96f1db16f649fc21dd18e5b0918f6 [1] > Link: https://github.com/llvm/llvm-project/commit/1df5ea29b43690b6622db2cad7b745607ca4de6a [2] > Link: https://github.com/llvm/llvm-project/commit/7ffabb61a5569444b5ac9322e22e5471cc5e4a77 [3] > Signed-off-by: Nathan Chancellor <nathan@kernel.org> > --- > arch/riscv/Kconfig | 9 +++++++++ > lib/Kconfig.debug | 1 + > 2 files changed, 10 insertions(+) > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > index 72be1d8122a3..81b473cb47b0 100644 > --- a/arch/riscv/Kconfig > +++ b/arch/riscv/Kconfig > @@ -186,6 +186,15 @@ config RISCV_USE_LINKER_RELAXATION > # https://github.com/llvm/llvm-project/commit/6611d58f5bbcbec77262d392e2923e1d680f6985 > depends on !LD_IS_LLD || LLD_VERSION >= 150000 > > +# https://github.com/llvm/llvm-project/commit/bbc0f99f3bc96f1db16f649fc21dd18e5b0918f6 > +config ARCH_HAS_BROKEN_DWARF5 > + def_bool y > + depends on RISCV_USE_LINKER_RELAXATION > + # https://github.com/llvm/llvm-project/commit/1df5ea29b43690b6622db2cad7b745607ca4de6a > + depends on AS_IS_LLVM && AS_VERSION < 180000 > + # https://github.com/llvm/llvm-project/commit/7ffabb61a5569444b5ac9322e22e5471cc5e4a77 > + depends on LD_IS_LLD && LLD_VERSION < 180000 > + > config ARCH_MMAP_RND_BITS_MIN > default 18 if 64BIT > default 8 > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index cc7d53d9dc01..a0ebce05a368 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -282,6 +282,7 @@ config DEBUG_INFO_DWARF4 > config DEBUG_INFO_DWARF5 > bool "Generate DWARF Version 5 debuginfo" > select DEBUG_INFO > + depends on !ARCH_HAS_BROKEN_DWARF5 > depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > help > Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc > > -- > 2.43.0 > A comment and "depends on" condition introduced by commit 0a6de78cff600cb991f2a1b7ed376935871796a0 "lib/Kconfig.debug: Add check for non-constant .{s,u}leb128 support to DWARF5" can now be refined. > ib/Kconfig.debug > (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) AS_VERSION can now be 24100. Thanks for the comment. I just marked https://sourceware.org/bugzilla/show_bug.cgi?id=27215 (" as: Error: non-constant .uleb128 is not supported on riscv64") as resolved :) > +# Clang is known to generate .{s,u}leb128 with symbol deltas with DWARF5, which > +# some targets may not support: https://sourceware.org/bugzilla/show_bug.cgi?id=27215 This comment can be updated:)
On Thu, Nov 30, 2023 at 08:16:41AM -0800, Fangrui Song wrote: > On Wed, Nov 29, 2023 at 3:30 PM Nathan Chancellor <nathan@kernel.org> wrote: > > > > LLVM prior to 18.0.0 would generate incorrect debug info for DWARF5 due > > to linker relaxation, which was worked around in clang by defaulting > > RISC-V to DWARF4 [1]. Unfortunately, this workaround does not work for > > the kernel because the DWARF version can be independently changed from > > the default in Kconfig. > > > > Do not allow DWARF5 to be selected for RISC-V when using linker > > relaxation (ld.lld >= 15.0.0) and a version of LLVM that does not have > > the fixes (the integrated assembler [2] and ld.lld [3] < 18.0.0) > > necessary to generate the correct debug info. > > > > Link: https://github.com/llvm/llvm-project/commit/bbc0f99f3bc96f1db16f649fc21dd18e5b0918f6 [1] > > Link: https://github.com/llvm/llvm-project/commit/1df5ea29b43690b6622db2cad7b745607ca4de6a [2] > > Link: https://github.com/llvm/llvm-project/commit/7ffabb61a5569444b5ac9322e22e5471cc5e4a77 [3] > > Signed-off-by: Nathan Chancellor <nathan@kernel.org> > > --- > > arch/riscv/Kconfig | 9 +++++++++ > > lib/Kconfig.debug | 1 + > > 2 files changed, 10 insertions(+) > > > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > > index 72be1d8122a3..81b473cb47b0 100644 > > --- a/arch/riscv/Kconfig > > +++ b/arch/riscv/Kconfig > > @@ -186,6 +186,15 @@ config RISCV_USE_LINKER_RELAXATION > > # https://github.com/llvm/llvm-project/commit/6611d58f5bbcbec77262d392e2923e1d680f6985 > > depends on !LD_IS_LLD || LLD_VERSION >= 150000 > > > > +# https://github.com/llvm/llvm-project/commit/bbc0f99f3bc96f1db16f649fc21dd18e5b0918f6 > > +config ARCH_HAS_BROKEN_DWARF5 > > + def_bool y > > + depends on RISCV_USE_LINKER_RELAXATION > > + # https://github.com/llvm/llvm-project/commit/1df5ea29b43690b6622db2cad7b745607ca4de6a > > + depends on AS_IS_LLVM && AS_VERSION < 180000 > > + # https://github.com/llvm/llvm-project/commit/7ffabb61a5569444b5ac9322e22e5471cc5e4a77 > > + depends on LD_IS_LLD && LLD_VERSION < 180000 > > + > > config ARCH_MMAP_RND_BITS_MIN > > default 18 if 64BIT > > default 8 > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > index cc7d53d9dc01..a0ebce05a368 100644 > > --- a/lib/Kconfig.debug > > +++ b/lib/Kconfig.debug > > @@ -282,6 +282,7 @@ config DEBUG_INFO_DWARF4 > > config DEBUG_INFO_DWARF5 > > bool "Generate DWARF Version 5 debuginfo" > > select DEBUG_INFO > > + depends on !ARCH_HAS_BROKEN_DWARF5 > > depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > > help > > Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc > > > > -- > > 2.43.0 > > > > A comment and "depends on" condition introduced by commit > 0a6de78cff600cb991f2a1b7ed376935871796a0 "lib/Kconfig.debug: Add check > for non-constant .{s,u}leb128 support to DWARF5" > can now be refined. > > > ib/Kconfig.debug > > (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > > AS_VERSION can now be 24100. That will impact all architectures that use GNU as, even though the issue was really only seen on RISC-V. It probably doesn't matter since most architectures work with the integrated assembler and that is what we tell people to use but I think the current check will continue to work. Alternatively, I could do something like this but it is quite ugly and verbose :/ diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index a0ebce05a368..aea0ef5a5d1f 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -231,11 +231,6 @@ config DEBUG_INFO in the "Debug information" choice below, indicating that debug information will be generated for build targets. -# Clang is known to generate .{s,u}leb128 with symbol deltas with DWARF5, which -# some targets may not support: https://sourceware.org/bugzilla/show_bug.cgi?id=27215 -config AS_HAS_NON_CONST_LEB128 - def_bool $(as-instr,.uleb128 .Lexpr_end4 - .Lexpr_start3\n.Lexpr_start3:\n.Lexpr_end4:) - choice prompt "Debug information" depends on DEBUG_KERNEL @@ -258,7 +253,7 @@ config DEBUG_INFO_NONE config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT bool "Rely on the toolchain's implicit default DWARF version" select DEBUG_INFO - depends on !CC_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) + depends on !CC_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && ((!RISCV && AS_VERSION >= 23502) || (RISCV && AS_VERSION >= 24100))) help The implicit default version of DWARF debug info produced by a toolchain changes over time. @@ -283,7 +278,7 @@ config DEBUG_INFO_DWARF5 bool "Generate DWARF Version 5 debuginfo" select DEBUG_INFO depends on !ARCH_HAS_BROKEN_DWARF5 - depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) + depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && ((!RISCV && AS_VERSION >= 23502) || (RISCV && AS_VERSION >= 24100))) help Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc 5.0+ accepts the -gdwarf-5 flag but only had partial support for some
On Fri, Dec 1, 2023 at 11:49 AM Nathan Chancellor <nathan@kernel.org> wrote: > > On Thu, Nov 30, 2023 at 08:16:41AM -0800, Fangrui Song wrote: > > On Wed, Nov 29, 2023 at 3:30 PM Nathan Chancellor <nathan@kernel.org> wrote: > > > > > > LLVM prior to 18.0.0 would generate incorrect debug info for DWARF5 due > > > to linker relaxation, which was worked around in clang by defaulting > > > RISC-V to DWARF4 [1]. Unfortunately, this workaround does not work for > > > the kernel because the DWARF version can be independently changed from > > > the default in Kconfig. > > > > > > Do not allow DWARF5 to be selected for RISC-V when using linker > > > relaxation (ld.lld >= 15.0.0) and a version of LLVM that does not have > > > the fixes (the integrated assembler [2] and ld.lld [3] < 18.0.0) > > > necessary to generate the correct debug info. > > > > > > Link: https://github.com/llvm/llvm-project/commit/bbc0f99f3bc96f1db16f649fc21dd18e5b0918f6 [1] > > > Link: https://github.com/llvm/llvm-project/commit/1df5ea29b43690b6622db2cad7b745607ca4de6a [2] > > > Link: https://github.com/llvm/llvm-project/commit/7ffabb61a5569444b5ac9322e22e5471cc5e4a77 [3] > > > Signed-off-by: Nathan Chancellor <nathan@kernel.org> > > > --- > > > arch/riscv/Kconfig | 9 +++++++++ > > > lib/Kconfig.debug | 1 + > > > 2 files changed, 10 insertions(+) > > > > > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > > > index 72be1d8122a3..81b473cb47b0 100644 > > > --- a/arch/riscv/Kconfig > > > +++ b/arch/riscv/Kconfig > > > @@ -186,6 +186,15 @@ config RISCV_USE_LINKER_RELAXATION > > > # https://github.com/llvm/llvm-project/commit/6611d58f5bbcbec77262d392e2923e1d680f6985 > > > depends on !LD_IS_LLD || LLD_VERSION >= 150000 > > > > > > +# https://github.com/llvm/llvm-project/commit/bbc0f99f3bc96f1db16f649fc21dd18e5b0918f6 > > > +config ARCH_HAS_BROKEN_DWARF5 > > > + def_bool y > > > + depends on RISCV_USE_LINKER_RELAXATION > > > + # https://github.com/llvm/llvm-project/commit/1df5ea29b43690b6622db2cad7b745607ca4de6a > > > + depends on AS_IS_LLVM && AS_VERSION < 180000 > > > + # https://github.com/llvm/llvm-project/commit/7ffabb61a5569444b5ac9322e22e5471cc5e4a77 > > > + depends on LD_IS_LLD && LLD_VERSION < 180000 > > > + > > > config ARCH_MMAP_RND_BITS_MIN > > > default 18 if 64BIT > > > default 8 > > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > > index cc7d53d9dc01..a0ebce05a368 100644 > > > --- a/lib/Kconfig.debug > > > +++ b/lib/Kconfig.debug > > > @@ -282,6 +282,7 @@ config DEBUG_INFO_DWARF4 > > > config DEBUG_INFO_DWARF5 > > > bool "Generate DWARF Version 5 debuginfo" > > > select DEBUG_INFO > > > + depends on !ARCH_HAS_BROKEN_DWARF5 > > > depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > > > help > > > Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc > > > > > > -- > > > 2.43.0 > > > > > > > A comment and "depends on" condition introduced by commit > > 0a6de78cff600cb991f2a1b7ed376935871796a0 "lib/Kconfig.debug: Add check > > for non-constant .{s,u}leb128 support to DWARF5" > > can now be refined. > > > > > ib/Kconfig.debug > > > (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > > > > AS_VERSION can now be 24100. > > That will impact all architectures that use GNU as, even though the > issue was really only seen on RISC-V. It probably doesn't matter since > most architectures work with the integrated assembler and that is what > we tell people to use but I think the current check will continue to > work. Agreed. depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) is enabled for GCC. The long condition chain is for Clang. Given Clang's behavior, we can simplify this to depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_HAS_NON_CONST_LEB128) This will still work even after R_LARCH_{ADD,SUB}_ULEB128 support is added to llvm-project. This condition matches HAVE_AS_LEB128 in GCC in spirit. > Alternatively, I could do something like this but it is quite ugly and > verbose :/ > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index a0ebce05a368..aea0ef5a5d1f 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -231,11 +231,6 @@ config DEBUG_INFO > in the "Debug information" choice below, indicating that debug > information will be generated for build targets. > > -# Clang is known to generate .{s,u}leb128 with symbol deltas with DWARF5, which > -# some targets may not support: https://sourceware.org/bugzilla/show_bug.cgi?id=27215 > -config AS_HAS_NON_CONST_LEB128 > - def_bool $(as-instr,.uleb128 .Lexpr_end4 - .Lexpr_start3\n.Lexpr_start3:\n.Lexpr_end4:) > - Consider keeping this config, but just reword the comment. > choice > prompt "Debug information" > depends on DEBUG_KERNEL > @@ -258,7 +253,7 @@ config DEBUG_INFO_NONE > config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT > bool "Rely on the toolchain's implicit default DWARF version" > select DEBUG_INFO > - depends on !CC_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > + depends on !CC_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && ((!RISCV && AS_VERSION >= 23502) || (RISCV && AS_VERSION >= 24100))) The RISCV condition would cause additional churn when LoongArch ULEB128 support is added. > help > The implicit default version of DWARF debug info produced by a > toolchain changes over time. > @@ -283,7 +278,7 @@ config DEBUG_INFO_DWARF5 > bool "Generate DWARF Version 5 debuginfo" > select DEBUG_INFO > depends on !ARCH_HAS_BROKEN_DWARF5 > - depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > + depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && ((!RISCV && AS_VERSION >= 23502) || (RISCV && AS_VERSION >= 24100))) > help > Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc > 5.0+ accepts the -gdwarf-5 flag but only had partial support for some
On Fri, Dec 01, 2023 at 12:12:26PM -0800, Fangrui Song wrote: > On Fri, Dec 1, 2023 at 11:49 AM Nathan Chancellor <nathan@kernel.org> wrote: > > > > On Thu, Nov 30, 2023 at 08:16:41AM -0800, Fangrui Song wrote: > > > On Wed, Nov 29, 2023 at 3:30 PM Nathan Chancellor <nathan@kernel.org> wrote: > > > > > > > > LLVM prior to 18.0.0 would generate incorrect debug info for DWARF5 due > > > > to linker relaxation, which was worked around in clang by defaulting > > > > RISC-V to DWARF4 [1]. Unfortunately, this workaround does not work for > > > > the kernel because the DWARF version can be independently changed from > > > > the default in Kconfig. > > > > > > > > Do not allow DWARF5 to be selected for RISC-V when using linker > > > > relaxation (ld.lld >= 15.0.0) and a version of LLVM that does not have > > > > the fixes (the integrated assembler [2] and ld.lld [3] < 18.0.0) > > > > necessary to generate the correct debug info. > > > > > > > > Link: https://github.com/llvm/llvm-project/commit/bbc0f99f3bc96f1db16f649fc21dd18e5b0918f6 [1] > > > > Link: https://github.com/llvm/llvm-project/commit/1df5ea29b43690b6622db2cad7b745607ca4de6a [2] > > > > Link: https://github.com/llvm/llvm-project/commit/7ffabb61a5569444b5ac9322e22e5471cc5e4a77 [3] > > > > Signed-off-by: Nathan Chancellor <nathan@kernel.org> > > > > --- > > > > arch/riscv/Kconfig | 9 +++++++++ > > > > lib/Kconfig.debug | 1 + > > > > 2 files changed, 10 insertions(+) > > > > > > > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > > > > index 72be1d8122a3..81b473cb47b0 100644 > > > > --- a/arch/riscv/Kconfig > > > > +++ b/arch/riscv/Kconfig > > > > @@ -186,6 +186,15 @@ config RISCV_USE_LINKER_RELAXATION > > > > # https://github.com/llvm/llvm-project/commit/6611d58f5bbcbec77262d392e2923e1d680f6985 > > > > depends on !LD_IS_LLD || LLD_VERSION >= 150000 > > > > > > > > +# https://github.com/llvm/llvm-project/commit/bbc0f99f3bc96f1db16f649fc21dd18e5b0918f6 > > > > +config ARCH_HAS_BROKEN_DWARF5 > > > > + def_bool y > > > > + depends on RISCV_USE_LINKER_RELAXATION > > > > + # https://github.com/llvm/llvm-project/commit/1df5ea29b43690b6622db2cad7b745607ca4de6a > > > > + depends on AS_IS_LLVM && AS_VERSION < 180000 > > > > + # https://github.com/llvm/llvm-project/commit/7ffabb61a5569444b5ac9322e22e5471cc5e4a77 > > > > + depends on LD_IS_LLD && LLD_VERSION < 180000 > > > > + > > > > config ARCH_MMAP_RND_BITS_MIN > > > > default 18 if 64BIT > > > > default 8 > > > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > > > index cc7d53d9dc01..a0ebce05a368 100644 > > > > --- a/lib/Kconfig.debug > > > > +++ b/lib/Kconfig.debug > > > > @@ -282,6 +282,7 @@ config DEBUG_INFO_DWARF4 > > > > config DEBUG_INFO_DWARF5 > > > > bool "Generate DWARF Version 5 debuginfo" > > > > select DEBUG_INFO > > > > + depends on !ARCH_HAS_BROKEN_DWARF5 > > > > depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > > > > help > > > > Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc > > > > > > > > -- > > > > 2.43.0 > > > > > > > > > > A comment and "depends on" condition introduced by commit > > > 0a6de78cff600cb991f2a1b7ed376935871796a0 "lib/Kconfig.debug: Add check > > > for non-constant .{s,u}leb128 support to DWARF5" > > > can now be refined. > > > > > > > ib/Kconfig.debug > > > > (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > > > > > > AS_VERSION can now be 24100. > > > > That will impact all architectures that use GNU as, even though the > > issue was really only seen on RISC-V. It probably doesn't matter since > > most architectures work with the integrated assembler and that is what > > we tell people to use but I think the current check will continue to > > work. > > Agreed. > > depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION > >= 23502 && AS_HAS_NON_CONST_LEB128) > > is enabled for GCC. The long condition chain is for Clang. Given > Clang's behavior, we can simplify this to > > depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && > AS_HAS_NON_CONST_LEB128) I think we still need the version check due to https://sourceware.org/bugzilla/show_bug.cgi?id=25611, which was added in commit 98cd6f521f10 ("Kconfig: allow explicit opt in to DWARF v5"). > This will still work even after R_LARCH_{ADD,SUB}_ULEB128 support is > added to llvm-project. > This condition matches HAVE_AS_LEB128 in GCC in spirit. > > > Alternatively, I could do something like this but it is quite ugly and > > verbose :/ > > > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > index a0ebce05a368..aea0ef5a5d1f 100644 > > --- a/lib/Kconfig.debug > > +++ b/lib/Kconfig.debug > > @@ -231,11 +231,6 @@ config DEBUG_INFO > > in the "Debug information" choice below, indicating that debug > > information will be generated for build targets. > > > > -# Clang is known to generate .{s,u}leb128 with symbol deltas with DWARF5, which > > -# some targets may not support: https://sourceware.org/bugzilla/show_bug.cgi?id=27215 > > -config AS_HAS_NON_CONST_LEB128 > > - def_bool $(as-instr,.uleb128 .Lexpr_end4 - .Lexpr_start3\n.Lexpr_start3:\n.Lexpr_end4:) > > - > > Consider keeping this config, but just reword the comment. Do you have a suggestion for how it should be reworded? I am struggling to come up with something that conveys additional information in a succinct manner. > > choice > > prompt "Debug information" > > depends on DEBUG_KERNEL > > @@ -258,7 +253,7 @@ config DEBUG_INFO_NONE > > config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT > > bool "Rely on the toolchain's implicit default DWARF version" > > select DEBUG_INFO > > - depends on !CC_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > > + depends on !CC_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && ((!RISCV && AS_VERSION >= 23502) || (RISCV && AS_VERSION >= 24100))) > > The RISCV condition would cause additional churn when LoongArch > ULEB128 support is added. Ah, I did not realize that LoongArch would have the same issue. This is definitely not the right way to go for that then. > > help > > The implicit default version of DWARF debug info produced by a > > toolchain changes over time. > > @@ -283,7 +278,7 @@ config DEBUG_INFO_DWARF5 > > bool "Generate DWARF Version 5 debuginfo" > > select DEBUG_INFO > > depends on !ARCH_HAS_BROKEN_DWARF5 > > - depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > > + depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && ((!RISCV && AS_VERSION >= 23502) || (RISCV && AS_VERSION >= 24100))) > > help > > Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc > > 5.0+ accepts the -gdwarf-5 flag but only had partial support for some Cheers, Nathan
On Fri, Dec 1, 2023 at 1:50 PM Nathan Chancellor <nathan@kernel.org> wrote: > > On Fri, Dec 01, 2023 at 12:12:26PM -0800, Fangrui Song wrote: > > On Fri, Dec 1, 2023 at 11:49 AM Nathan Chancellor <nathan@kernel.org> wrote: > > > > > > On Thu, Nov 30, 2023 at 08:16:41AM -0800, Fangrui Song wrote: > > > > On Wed, Nov 29, 2023 at 3:30 PM Nathan Chancellor <nathan@kernel.org> wrote: > > > > > > > > > > LLVM prior to 18.0.0 would generate incorrect debug info for DWARF5 due > > > > > to linker relaxation, which was worked around in clang by defaulting > > > > > RISC-V to DWARF4 [1]. Unfortunately, this workaround does not work for > > > > > the kernel because the DWARF version can be independently changed from > > > > > the default in Kconfig. > > > > > > > > > > Do not allow DWARF5 to be selected for RISC-V when using linker > > > > > relaxation (ld.lld >= 15.0.0) and a version of LLVM that does not have > > > > > the fixes (the integrated assembler [2] and ld.lld [3] < 18.0.0) > > > > > necessary to generate the correct debug info. > > > > > > > > > > Link: https://github.com/llvm/llvm-project/commit/bbc0f99f3bc96f1db16f649fc21dd18e5b0918f6 [1] > > > > > Link: https://github.com/llvm/llvm-project/commit/1df5ea29b43690b6622db2cad7b745607ca4de6a [2] > > > > > Link: https://github.com/llvm/llvm-project/commit/7ffabb61a5569444b5ac9322e22e5471cc5e4a77 [3] > > > > > Signed-off-by: Nathan Chancellor <nathan@kernel.org> > > > > > --- > > > > > arch/riscv/Kconfig | 9 +++++++++ > > > > > lib/Kconfig.debug | 1 + > > > > > 2 files changed, 10 insertions(+) > > > > > > > > > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > > > > > index 72be1d8122a3..81b473cb47b0 100644 > > > > > --- a/arch/riscv/Kconfig > > > > > +++ b/arch/riscv/Kconfig > > > > > @@ -186,6 +186,15 @@ config RISCV_USE_LINKER_RELAXATION > > > > > # https://github.com/llvm/llvm-project/commit/6611d58f5bbcbec77262d392e2923e1d680f6985 > > > > > depends on !LD_IS_LLD || LLD_VERSION >= 150000 > > > > > > > > > > +# https://github.com/llvm/llvm-project/commit/bbc0f99f3bc96f1db16f649fc21dd18e5b0918f6 > > > > > +config ARCH_HAS_BROKEN_DWARF5 > > > > > + def_bool y > > > > > + depends on RISCV_USE_LINKER_RELAXATION > > > > > + # https://github.com/llvm/llvm-project/commit/1df5ea29b43690b6622db2cad7b745607ca4de6a > > > > > + depends on AS_IS_LLVM && AS_VERSION < 180000 > > > > > + # https://github.com/llvm/llvm-project/commit/7ffabb61a5569444b5ac9322e22e5471cc5e4a77 > > > > > + depends on LD_IS_LLD && LLD_VERSION < 180000 > > > > > + > > > > > config ARCH_MMAP_RND_BITS_MIN > > > > > default 18 if 64BIT > > > > > default 8 > > > > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > > > > index cc7d53d9dc01..a0ebce05a368 100644 > > > > > --- a/lib/Kconfig.debug > > > > > +++ b/lib/Kconfig.debug > > > > > @@ -282,6 +282,7 @@ config DEBUG_INFO_DWARF4 > > > > > config DEBUG_INFO_DWARF5 > > > > > bool "Generate DWARF Version 5 debuginfo" > > > > > select DEBUG_INFO > > > > > + depends on !ARCH_HAS_BROKEN_DWARF5 > > > > > depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > > > > > help > > > > > Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc > > > > > > > > > > -- > > > > > 2.43.0 > > > > > > > > > > > > > A comment and "depends on" condition introduced by commit > > > > 0a6de78cff600cb991f2a1b7ed376935871796a0 "lib/Kconfig.debug: Add check > > > > for non-constant .{s,u}leb128 support to DWARF5" > > > > can now be refined. > > > > > > > > > ib/Kconfig.debug > > > > > (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > > > > > > > > AS_VERSION can now be 24100. > > > > > > That will impact all architectures that use GNU as, even though the > > > issue was really only seen on RISC-V. It probably doesn't matter since > > > most architectures work with the integrated assembler and that is what > > > we tell people to use but I think the current check will continue to > > > work. > > > > Agreed. > > > > depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION > > >= 23502 && AS_HAS_NON_CONST_LEB128) > > > > is enabled for GCC. The long condition chain is for Clang. Given > > Clang's behavior, we can simplify this to > > > > depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && > > AS_HAS_NON_CONST_LEB128) > > I think we still need the version check due to > https://sourceware.org/bugzilla/show_bug.cgi?id=25611, which was added > in commit 98cd6f521f10 ("Kconfig: allow explicit opt in to DWARF v5"). I see... > > This will still work even after R_LARCH_{ADD,SUB}_ULEB128 support is > > added to llvm-project. > > This condition matches HAVE_AS_LEB128 in GCC in spirit. > > > > > Alternatively, I could do something like this but it is quite ugly and > > > verbose :/ > > > > > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > > index a0ebce05a368..aea0ef5a5d1f 100644 > > > --- a/lib/Kconfig.debug > > > +++ b/lib/Kconfig.debug > > > @@ -231,11 +231,6 @@ config DEBUG_INFO > > > in the "Debug information" choice below, indicating that debug > > > information will be generated for build targets. > > > > > > -# Clang is known to generate .{s,u}leb128 with symbol deltas with DWARF5, which > > > -# some targets may not support: https://sourceware.org/bugzilla/show_bug.cgi?id=27215 > > > -config AS_HAS_NON_CONST_LEB128 > > > - def_bool $(as-instr,.uleb128 .Lexpr_end4 - .Lexpr_start3\n.Lexpr_start3:\n.Lexpr_end4:) > > > - > > > > Consider keeping this config, but just reword the comment. > > Do you have a suggestion for how it should be reworded? I am struggling > to come up with something that conveys additional information in a > succinct manner. Perhaps: Clang generates .uleb128 with label differences for DWARF v5, a feature that older binutils ports, utilizing RISC-V style linker relaxation, do not support. (Signed LEB128 is used by DWARF as well, but it is encoded directly into DW_OP_fbreg/DW_LNS_advance_line/etc, and explicit .sleb128 directives are not emitted) (In assemblers, "label difference" is a more common term.) (People working on DWARF tend to prefer DWARF v5 to DWARF5, when the full "DWARF version 5" feels too verbose.) > > > choice > > > prompt "Debug information" > > > depends on DEBUG_KERNEL > > > @@ -258,7 +253,7 @@ config DEBUG_INFO_NONE > > > config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT > > > bool "Rely on the toolchain's implicit default DWARF version" > > > select DEBUG_INFO > > > - depends on !CC_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > > > + depends on !CC_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && ((!RISCV && AS_VERSION >= 23502) || (RISCV && AS_VERSION >= 24100))) > > > > The RISCV condition would cause additional churn when LoongArch > > ULEB128 support is added. > > Ah, I did not realize that LoongArch would have the same issue. This is > definitely not the right way to go for that then. > > > > help > > > The implicit default version of DWARF debug info produced by a > > > toolchain changes over time. > > > @@ -283,7 +278,7 @@ config DEBUG_INFO_DWARF5 > > > bool "Generate DWARF Version 5 debuginfo" > > > select DEBUG_INFO > > > depends on !ARCH_HAS_BROKEN_DWARF5 > > > - depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > > > + depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && ((!RISCV && AS_VERSION >= 23502) || (RISCV && AS_VERSION >= 24100))) > > > help > > > Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc > > > 5.0+ accepts the -gdwarf-5 flag but only had partial support for some > > Cheers, > Nathan >
On Fri, Dec 01, 2023 at 08:31:12PM -0800, Fangrui Song wrote: > Perhaps: Clang generates .uleb128 with label differences for DWARF v5, > a feature that older binutils ports, utilizing RISC-V style linker > relaxation, do not support. > > (Signed LEB128 is used by DWARF as well, but it is encoded directly > into DW_OP_fbreg/DW_LNS_advance_line/etc, and explicit .sleb128 > directives are not emitted) > (In assemblers, "label difference" is a more common term.) > (People working on DWARF tend to prefer DWARF v5 to DWARF5, when the > full "DWARF version 5" feels too verbose.) Thanks, does this diff seem reasonable to you? I'd like to keep the issue link as a paper trail and I figured that we might as well make the configuration name slightly more accurate with that additional information. I will send it as a separate patch in v2 tomorrow if so in order to give people a chance to further chime in on the series. Cheers, Nathan diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index a0ebce05a368..76c2cc697573 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -231,9 +231,10 @@ config DEBUG_INFO in the "Debug information" choice below, indicating that debug information will be generated for build targets. -# Clang is known to generate .{s,u}leb128 with symbol deltas with DWARF5, which -# some targets may not support: https://sourceware.org/bugzilla/show_bug.cgi?id=27215 -config AS_HAS_NON_CONST_LEB128 +# Clang generates .uleb128 with label differences for DWARF v5, a feature that +# older binutils ports do not support when utilizing RISC-V style linker +# relaxation: https://sourceware.org/bugzilla/show_bug.cgi?id=27215 +config AS_HAS_NON_CONST_ULEB128 def_bool $(as-instr,.uleb128 .Lexpr_end4 - .Lexpr_start3\n.Lexpr_start3:\n.Lexpr_end4:) choice @@ -258,7 +259,7 @@ config DEBUG_INFO_NONE config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT bool "Rely on the toolchain's implicit default DWARF version" select DEBUG_INFO - depends on !CC_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) + depends on !CC_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_ULEB128) help The implicit default version of DWARF debug info produced by a toolchain changes over time. @@ -283,7 +284,7 @@ config DEBUG_INFO_DWARF5 bool "Generate DWARF Version 5 debuginfo" select DEBUG_INFO depends on !ARCH_HAS_BROKEN_DWARF5 - depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) + depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_ULEB128) help Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc 5.0+ accepts the -gdwarf-5 flag but only had partial support for some
On Mon, Dec 4, 2023 at 3:12 PM Nathan Chancellor <nathan@kernel.org> wrote: > > On Fri, Dec 01, 2023 at 08:31:12PM -0800, Fangrui Song wrote: > > Perhaps: Clang generates .uleb128 with label differences for DWARF v5, > > a feature that older binutils ports, utilizing RISC-V style linker > > relaxation, do not support. > > > > (Signed LEB128 is used by DWARF as well, but it is encoded directly > > into DW_OP_fbreg/DW_LNS_advance_line/etc, and explicit .sleb128 > > directives are not emitted) > > (In assemblers, "label difference" is a more common term.) > > (People working on DWARF tend to prefer DWARF v5 to DWARF5, when the > > full "DWARF version 5" feels too verbose.) > > Thanks, does this diff seem reasonable to you? I'd like to keep the > issue link as a paper trail and I figured that we might as well make the > configuration name slightly more accurate with that additional > information. I will send it as a separate patch in v2 tomorrow if so in > order to give people a chance to further chime in on the series. > > Cheers, > Nathan > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index a0ebce05a368..76c2cc697573 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -231,9 +231,10 @@ config DEBUG_INFO > in the "Debug information" choice below, indicating that debug > information will be generated for build targets. > > -# Clang is known to generate .{s,u}leb128 with symbol deltas with DWARF5, which > -# some targets may not support: https://sourceware.org/bugzilla/show_bug.cgi?id=27215 > -config AS_HAS_NON_CONST_LEB128 > +# Clang generates .uleb128 with label differences for DWARF v5, a feature that > +# older binutils ports do not support when utilizing RISC-V style linker > +# relaxation: https://sourceware.org/bugzilla/show_bug.cgi?id=27215 > +config AS_HAS_NON_CONST_ULEB128 > def_bool $(as-instr,.uleb128 .Lexpr_end4 - .Lexpr_start3\n.Lexpr_start3:\n.Lexpr_end4:) > > choice > @@ -258,7 +259,7 @@ config DEBUG_INFO_NONE > config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT > bool "Rely on the toolchain's implicit default DWARF version" > select DEBUG_INFO > - depends on !CC_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > + depends on !CC_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_ULEB128) > help > The implicit default version of DWARF debug info produced by a > toolchain changes over time. > @@ -283,7 +284,7 @@ config DEBUG_INFO_DWARF5 > bool "Generate DWARF Version 5 debuginfo" > select DEBUG_INFO > depends on !ARCH_HAS_BROKEN_DWARF5 > - depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) > + depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_ULEB128) > help > Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc > 5.0+ accepts the -gdwarf-5 flag but only had partial support for some This diff looks good to me.
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 72be1d8122a3..81b473cb47b0 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -186,6 +186,15 @@ config RISCV_USE_LINKER_RELAXATION # https://github.com/llvm/llvm-project/commit/6611d58f5bbcbec77262d392e2923e1d680f6985 depends on !LD_IS_LLD || LLD_VERSION >= 150000 +# https://github.com/llvm/llvm-project/commit/bbc0f99f3bc96f1db16f649fc21dd18e5b0918f6 +config ARCH_HAS_BROKEN_DWARF5 + def_bool y + depends on RISCV_USE_LINKER_RELAXATION + # https://github.com/llvm/llvm-project/commit/1df5ea29b43690b6622db2cad7b745607ca4de6a + depends on AS_IS_LLVM && AS_VERSION < 180000 + # https://github.com/llvm/llvm-project/commit/7ffabb61a5569444b5ac9322e22e5471cc5e4a77 + depends on LD_IS_LLD && LLD_VERSION < 180000 + config ARCH_MMAP_RND_BITS_MIN default 18 if 64BIT default 8 diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index cc7d53d9dc01..a0ebce05a368 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -282,6 +282,7 @@ config DEBUG_INFO_DWARF4 config DEBUG_INFO_DWARF5 bool "Generate DWARF Version 5 debuginfo" select DEBUG_INFO + depends on !ARCH_HAS_BROKEN_DWARF5 depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) help Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc
LLVM prior to 18.0.0 would generate incorrect debug info for DWARF5 due to linker relaxation, which was worked around in clang by defaulting RISC-V to DWARF4 [1]. Unfortunately, this workaround does not work for the kernel because the DWARF version can be independently changed from the default in Kconfig. Do not allow DWARF5 to be selected for RISC-V when using linker relaxation (ld.lld >= 15.0.0) and a version of LLVM that does not have the fixes (the integrated assembler [2] and ld.lld [3] < 18.0.0) necessary to generate the correct debug info. Link: https://github.com/llvm/llvm-project/commit/bbc0f99f3bc96f1db16f649fc21dd18e5b0918f6 [1] Link: https://github.com/llvm/llvm-project/commit/1df5ea29b43690b6622db2cad7b745607ca4de6a [2] Link: https://github.com/llvm/llvm-project/commit/7ffabb61a5569444b5ac9322e22e5471cc5e4a77 [3] Signed-off-by: Nathan Chancellor <nathan@kernel.org> --- arch/riscv/Kconfig | 9 +++++++++ lib/Kconfig.debug | 1 + 2 files changed, 10 insertions(+)