| Message ID | 20180515141124.84254-2-namit@vmware.com (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
On Tue, May 15, 2018 at 07:11:08AM -0700, Nadav Amit wrote: > GCC considers the number of statements in inlined assembly blocks, > according to new-lines and semicolons, as an indication to the cost of > the block in time and space. This data is distorted by the kernel code, > which puts information in alternative sections. As a result, the > compiler may perform incorrect inlining and branch optimizations. > > In the case of objtool, this distortion is extreme, since anyhow the > annotations of objtool are discarded during linkage. > > The solution is to set an assembly macro and call it from the inlinedv > assembly block. As a result GCC considers the inline assembly block as > a single instruction. > > This patch slightly increases the kernel size. > > text data bss dec hex filename > 18126699 10066728 2936832 31130259 1db0293 ./vmlinux before > 18126824 10067268 2936832 31130924 1db052c ./vmlinux after (+665) With what kernel config? What's the text size change for an allnoconfig? -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Josh Triplett <josh@joshtriplett.org> wrote: > On Tue, May 15, 2018 at 07:11:08AM -0700, Nadav Amit wrote: >> GCC considers the number of statements in inlined assembly blocks, >> according to new-lines and semicolons, as an indication to the cost of >> the block in time and space. This data is distorted by the kernel code, >> which puts information in alternative sections. As a result, the >> compiler may perform incorrect inlining and branch optimizations. >> >> In the case of objtool, this distortion is extreme, since anyhow the >> annotations of objtool are discarded during linkage. >> >> The solution is to set an assembly macro and call it from the inlinedv >> assembly block. As a result GCC considers the inline assembly block as >> a single instruction. >> >> This patch slightly increases the kernel size. >> >> text data bss dec hex filename >> 18126699 10066728 2936832 31130259 1db0293 ./vmlinux before >> 18126824 10067268 2936832 31130924 1db052c ./vmlinux after (+665) > > With what kernel config? What's the text size change for an allnoconfig? I use my custom config and to include the drivers in the image. Other configs were not too appropriate: defconfig does not enable paravirt and allyesconfig is too heavy. There is no effect with allnoconfig on size: text data bss dec hex filename 1018441 230148 1215604 2464193 2599c1 ./vmlinux 1018441 230148 1215604 2464193 2599c1 ./vmlinux I think it is expected since CONFIG_STACK_VALIDATION is off. No? Thanks, Nadav -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, May 15, 2018 at 02:53:52PM -0700, Nadav Amit wrote: > Josh Triplett <josh@joshtriplett.org> wrote: > > > On Tue, May 15, 2018 at 07:11:08AM -0700, Nadav Amit wrote: > >> GCC considers the number of statements in inlined assembly blocks, > >> according to new-lines and semicolons, as an indication to the cost of > >> the block in time and space. This data is distorted by the kernel code, > >> which puts information in alternative sections. As a result, the > >> compiler may perform incorrect inlining and branch optimizations. > >> > >> In the case of objtool, this distortion is extreme, since anyhow the > >> annotations of objtool are discarded during linkage. > >> > >> The solution is to set an assembly macro and call it from the inlinedv > >> assembly block. As a result GCC considers the inline assembly block as > >> a single instruction. > >> > >> This patch slightly increases the kernel size. > >> > >> text data bss dec hex filename > >> 18126699 10066728 2936832 31130259 1db0293 ./vmlinux before > >> 18126824 10067268 2936832 31130924 1db052c ./vmlinux after (+665) > > > > With what kernel config? What's the text size change for an allnoconfig? > > I use my custom config and to include the drivers in the image. Other > configs were not too appropriate: defconfig does not enable paravirt and > allyesconfig is too heavy. > > There is no effect with allnoconfig on size: > > text data bss dec hex filename > 1018441 230148 1215604 2464193 2599c1 ./vmlinux > 1018441 230148 1215604 2464193 2599c1 ./vmlinux > > I think it is expected since CONFIG_STACK_VALIDATION is off. No? Thanks for checking; fine by me then. :) -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/linux/compiler.h b/include/linux/compiler.h index ab4711c63601..369753000541 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -98,17 +98,30 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, * The __COUNTER__ based labels are a hack to make each instance of the macros * unique, to convince GCC not to merge duplicate inline asm statements. */ + +asm ("\n" + ".macro __annotate_reachable counter:req\n" + "\\counter:\n\t" + ".pushsection .discard.reachable\n\t" + ".long \\counter\\()b -.\n\t" + ".popsection\n" + ".endm\n"); + #define annotate_reachable() ({ \ - asm volatile("%c0:\n\t" \ - ".pushsection .discard.reachable\n\t" \ - ".long %c0b - .\n\t" \ - ".popsection\n\t" : : "i" (__COUNTER__)); \ + asm volatile("__annotate_reachable %c0" : : "i" (__COUNTER__)); \ }) + +asm ("\n" + ".macro __annotate_unreachable counter:req\n" + "\\counter:\n\t" + ".pushsection .discard.unreachable\n\t" + ".long \\counter\\()b -.\n\t" + ".popsection\n" + ".endm"); + #define annotate_unreachable() ({ \ - asm volatile("%c0:\n\t" \ - ".pushsection .discard.unreachable\n\t" \ - ".long %c0b - .\n\t" \ - ".popsection\n\t" : : "i" (__COUNTER__)); \ + asm volatile("__annotate_unreachable %c0" : : \ + "i" (__COUNTER__)); \ }) #define ASM_UNREACHABLE \ "999:\n\t" \
GCC considers the number of statements in inlined assembly blocks, according to new-lines and semicolons, as an indication to the cost of the block in time and space. This data is distorted by the kernel code, which puts information in alternative sections. As a result, the compiler may perform incorrect inlining and branch optimizations. In the case of objtool, this distortion is extreme, since anyhow the annotations of objtool are discarded during linkage. The solution is to set an assembly macro and call it from the inlinedv assembly block. As a result GCC considers the inline assembly block as a single instruction. This patch slightly increases the kernel size. text data bss dec hex filename 18126699 10066728 2936832 31130259 1db0293 ./vmlinux before 18126824 10067268 2936832 31130924 1db052c ./vmlinux after (+665) But allows more aggressive inlining. Static text symbols: Before: 40033 After: 40015 (-18) Cc: Christopher Li <sparse@chrisli.org> Cc: linux-sparse@vger.kernel.org Signed-off-by: Nadav Amit <namit@vmware.com> --- include/linux/compiler.h | 29 +++++++++++++++++++++-------- 1 file changed, 21 insertions(+), 8 deletions(-)