diff options
Diffstat (limited to 'tools/objtool/Documentation')
| -rw-r--r-- | tools/objtool/Documentation/stack-validation.txt | 38 |
1 files changed, 29 insertions, 9 deletions
diff --git a/tools/objtool/Documentation/stack-validation.txt b/tools/objtool/Documentation/stack-validation.txt index 5a95896105bc..55a60d331f47 100644 --- a/tools/objtool/Documentation/stack-validation.txt +++ b/tools/objtool/Documentation/stack-validation.txt @@ -299,18 +299,38 @@ they mean, and suggestions for how to fix them. Errors in .c files ------------------ -If you're getting an objtool error in a compiled .c file, chances are -the file uses an asm() statement which has a "call" instruction. An -asm() statement with a call instruction must declare the use of the -stack pointer in its output operand. For example, on x86_64: +1. c_file.o: warning: objtool: funcA() falls through to next function funcB() - register void *__sp asm("rsp"); - asm volatile("call func" : "+r" (__sp)); + This means that funcA() doesn't end with a return instruction or an + unconditional jump, and that objtool has determined that the function + can fall through into the next function. There could be different + reasons for this: -Otherwise the stack frame may not get created before the call. + 1) funcA()'s last instruction is a call to a "noreturn" function like + panic(). In this case the noreturn function needs to be added to + objtool's hard-coded global_noreturns array. Feel free to bug the + objtool maintainer, or you can submit a patch. -Another possible cause for errors in C code is if the Makefile removes --fno-omit-frame-pointer or adds -fomit-frame-pointer to the gcc options. + 2) funcA() uses the unreachable() annotation in a section of code + that is actually reachable. + + 3) If funcA() calls an inline function, the object code for funcA() + might be corrupt due to a gcc bug. For more details, see: + https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646 + +2. If you're getting any other objtool error in a compiled .c file, it + may be because the file uses an asm() statement which has a "call" + instruction. An asm() statement with a call instruction must declare + the use of the stack pointer in its output operand. For example, on + x86_64: + + register void *__sp asm("rsp"); + asm volatile("call func" : "+r" (__sp)); + + Otherwise the stack frame may not get created before the call. + +3. Another possible cause for errors in C code is if the Makefile removes + -fno-omit-frame-pointer or adds -fomit-frame-pointer to the gcc options. Also see the above section for .S file errors for more information what the individual error messages mean. |