| Message ID | 20221014164756.843991-1-ndesaulniers@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] kbuild: add -fno-discard-value-names to cmd_cc_ll_c | expand |
diff --git a/scripts/Makefile.build b/scripts/Makefile.build index 22adbf89cb31..41f3602fc8de 100644 --- a/scripts/Makefile.build +++ b/scripts/Makefile.build @@ -140,7 +140,7 @@ $(obj)/%.symtypes : $(src)/%.c FORCE # LLVM assembly # Generate .ll files from .c quiet_cmd_cc_ll_c = CC $(quiet_modtag) $@ - cmd_cc_ll_c = $(CC) $(c_flags) -emit-llvm -S -o $@ $< + cmd_cc_ll_c = $(CC) $(c_flags) -emit-llvm -S -fno-discard-value-names -o $@ $< $(obj)/%.ll: $(src)/%.c FORCE $(call if_changed_dep,cc_ll_c)
When debugging LLVM IR, it can be handy for clang to not discard value names used for local variables and parameters. Compare the generated IR. -fdiscard-value-names: define i32 @core_sys_select(i32 %0, ptr %1, ptr %2, ptr %3, ptr %4) { %6 = alloca i64 %7 = alloca %struct.poll_wqueues %8 = alloca [64 x i32] -fno-discard-value-names: define i32 @core_sys_select(i32 %n, ptr %inp, ptr %outp, ptr %exp, ptr %end_time) { %expire.i = alloca i64 %table.i = alloca %struct.poll_wqueues %stack_fds = alloca [64 x i32] The rule for generating human readable LLVM IR (.ll) is only useful as a debugging feature: $ make LLVM=1 fs/select.ll As Fangrui notes: A LLVM_ENABLE_ASSERTIONS=off build of Clang defaults to -fdiscard-value-names. A LLVM_ENABLE_ASSERTIONS=on build of Clang defaults to -fno-discard-value-names. Explicitly enable -fdiscard-value-names so that the IR always contains value names regardless of whether assertions were enabled or not. Assertions generally are not enabled in releases of clang packaged by distributions. Link: https://github.com/ClangBuiltLinux/linux/issues/1467 Reviewed-by: Nathan Chancellor <nathan@kernel.org> Reviewed-by: Fangrui Song <maskray@google.com> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> --- Changes v1 -> v2: * Only update commit message: * Pick up Nathan & Fangrui's RB tags. * Add link (I forgot I filed a bug about this a while ago!). * Add note from Fangrui. * Add final paragraph. scripts/Makefile.build | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)