| Message ID | 20240728203001.2551083-3-xur@google.com |
|---|---|
| State | New |
| Headers | show |
| Series | Add AutoFDO and Propeller support for Clang build | expand |
On Sun, Jul 28, 2024 at 01:29:55PM -0700, Rong Xu wrote: > In the presence of both weak and strong function definitions, the > linker drops the weak symbol in favor of a strong symbol, but > leaves the code in place. Code in ignore_unreachable_insn() has > some heuristics to suppress the warning, but it does not work when > -ffunction-sections is enabled. > > Suppose function foo has both strong and weak definitions. > Case 1: The strong definition has an annotated section name, > like .init.text. Only the weak definition will be placed into > .text.foo. But since the section has no symbols, there will be no > "hole" in the section. > > Case 2: Both sections are without an annotated section name. > Both will be placed into .text.foo section, but there will be only one > symbol (the strong one). If the weak code is before the strong code, > there is no "hole" as it fails to find the right-most symbol before > the offset. > > The fix is to use the first node to compute the hole if hole.sym > is empty. If there is no symbol in the section, the first node > will be NULL, in which case, -1 is returned to skip the whole > section. > > Co-developed-by: Han Shen <shenhan@google.com> > Signed-off-by: Han Shen <shenhan@google.com> > Signed-off-by: Rong Xu <xur@google.com> > Suggested-by: Sriraman Tallam <tmsriram@google.com> > Suggested-by: Krzysztof Pszeniczny <kpszeniczny@google.com> > --- > tools/objtool/elf.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c > index 3d27983dc908..fa88bb254ccc 100644 > --- a/tools/objtool/elf.c > +++ b/tools/objtool/elf.c > @@ -224,12 +224,15 @@ int find_symbol_hole_containing(const struct section *sec, unsigned long offset) > if (n) > return 0; /* not a hole */ > > - /* didn't find a symbol for which @offset is after it */ > - if (!hole.sym) > - return 0; /* not a hole */ > + /* > + * @offset >= sym->offset + sym->len, find symbol after it. > + * Use the first node in rb_tree when hole.sym is NULL. > + */ /* * If we are not right of any symbol, the next symbol must be * the first symbol. Either way, the next symbol -- if there is * one -- provides the rightmost boundary of the hole. */ if (!hole.sym) n = rb_first_cached(&sec->symbol_tree); else n = rb_next(&hole.sym->node); That tells us more of why, rather than of what. Hmm? > + if (hole.sym) > + n = rb_next(&hole.sym->node); > + else > + n = rb_first_cached(&sec->symbol_tree); > > - /* @offset >= sym->offset + sym->len, find symbol after it */ > - n = rb_next(&hole.sym->node); > if (!n) > return -1; /* until end of address space */ > > -- > 2.46.0.rc1.232.g9752f9e123-goog >
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c index 3d27983dc908..fa88bb254ccc 100644 --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -224,12 +224,15 @@ int find_symbol_hole_containing(const struct section *sec, unsigned long offset) if (n) return 0; /* not a hole */ - /* didn't find a symbol for which @offset is after it */ - if (!hole.sym) - return 0; /* not a hole */ + /* + * @offset >= sym->offset + sym->len, find symbol after it. + * Use the first node in rb_tree when hole.sym is NULL. + */ + if (hole.sym) + n = rb_next(&hole.sym->node); + else + n = rb_first_cached(&sec->symbol_tree); - /* @offset >= sym->offset + sym->len, find symbol after it */ - n = rb_next(&hole.sym->node); if (!n) return -1; /* until end of address space */