On Wed, Jun 17, 2020 at 2:27 PM Fāng-ruì Sòng <maskray@xxxxxxxxxx> wrote: > > > On 2020-06-17, Nick Desaulniers wrote: > >ld.bfd's internal linker script considers .text.hot AND .text.hot.* to > >be part of .text, as well as .text.unlikely and .text.unlikely.*. > > >ld.lld will produce .text.hot.*/.text.unlikely.* sections. > > Correction to this sentence. lld is not relevant here. > > -ffunction-sections combined with profile-guided optimization can > produce .text.hot.* .text.unlikely.* sections. Newer clang may produce > .text.hot. .text.unlikely. (without suffix, but with a trailing dot) > when -fno-unique-section-names is specified, as an optimization to make > .strtab smaller. Then why was the bug report reporting https://reviews.llvm.org/D79600 as the result of a bisection, if LLD is not relevant? Was the bisection wrong? The upstream report wasn't initially public, for no good reason. So I didn't include it, but if we end up taking v1, this should have Link: https://bugs.chromium.org/p/chromium/issues/detail?id=1084760 The kernel doesn't use -fno-unique-section-names; is that another flag that's added by CrOS' compiler wrapper? https://source.chromium.org/chromiumos/chromiumos/codesearch/+/master:src/third_party/toolchain-utils/compiler_wrapper/config.go;l=110 Looks like no. It doesn't use `-fno-unique-section-names` or `-ffunction-sections`. > > We've already seen that GCC can place main in .text.startup without > -ffunction-sections. There may be other non -ffunction-sections cases > for .text.hot.* or .text.unlikely.*. So it is definitely a good idea to > be more specific even if we don't care about -ffunction-sections for > now. > > >Make sure to group these together. Otherwise these orphan sections may > >be placed outside of the the _stext/_etext boundaries. > > > >Cc: stable@xxxxxxxxxxxxxxx > >Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=add44f8d5c5c05e08b11e033127a744d61c26aee > >Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=1de778ed23ce7492c523d5850c6c6dbb34152655 > >Link: https://reviews.llvm.org/D79600 > >Reported-by: Jian Cai <jiancai@xxxxxxxxxx> > >Debugged-by: Luis Lozano <llozano@xxxxxxxxxx> > >Suggested-by: Fāng-ruì Sòng <maskray@xxxxxxxxxx> > >Tested-by: Luis Lozano <llozano@xxxxxxxxxx> > >Tested-by: Manoj Gupta <manojgupta@xxxxxxxxxx> > >Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > >--- > > include/asm-generic/vmlinux.lds.h | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > >diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > >index d7c7c7f36c4a..fe5aaef169e3 100644 > >--- a/include/asm-generic/vmlinux.lds.h > >+++ b/include/asm-generic/vmlinux.lds.h > >@@ -560,7 +560,9 @@ > > */ > > #define TEXT_TEXT \ > > ALIGN_FUNCTION(); \ > >- *(.text.hot TEXT_MAIN .text.fixup .text.unlikely) \ > >+ *(.text.hot .text.hot.*) \ > >+ *(TEXT_MAIN .text.fixup) \ > >+ *(.text.unlikely .text.unlikely.*) \ > > NOINSTR_TEXT \ > > *(.text..refcount) \ > > *(.ref.text) \ > >-- > >2.27.0.290.gba653c62da-goog > > -- Thanks, ~Nick Desaulniers
