Message ID | 20200528163541.7262-1-szabolcs.nagy@arm.com |
---|---|
State | New |
Headers | show |
Series | doc: Clarify __builtin_return_address [PR94891] | expand |
* Szabolcs Nagy: > diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi > index cced19d2018..0fd32a22599 100644 > --- a/gcc/doc/extend.texi > +++ b/gcc/doc/extend.texi > On some machines it may be impossible to determine the return address of > any function other than the current one; in such cases, or when the top > +of the stack has been reached, this function returns an unspecified > +value. Can it crash as well? But that's a pre-existing issue with the wording. > Additional post-processing of the returned value may be needed, see > @code{__builtin_extract_return_addr}. > > +The stored representation of the return address in memory may be different > +from the address returned by @code{__builtin_return_address}. For example > +on AArch64 the stored address may be mangled with return address signing. > + > Calling this function with a nonzero argument can have unpredictable > effects, including crashing the calling program. As a result, calls > that are considered unsafe are diagnosed when the @option{-Wframe-address} > option is in effect. Such calls should only be made in debugging > situations. > + > +On targets where code addresses are representable as @code{void *}, > +@smallexample > +void *addr = __builtin_extract_return_addr (__builtin_return_address (0)) > +@end smallexample > +gives the code address where the current function would return. For example > +such address may be used with @code{dladdr} or other interfaces that work > +with code addresses. > @end deftypefn The change looks reasonable to me. It is worded in such a way that it covers architectures which use function descriptors. Thanks, Florian
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi index cced19d2018..0fd32a22599 100644 --- a/gcc/doc/extend.texi +++ b/gcc/doc/extend.texi @@ -11151,18 +11151,30 @@ The @var{level} argument must be a constant integer. On some machines it may be impossible to determine the return address of any function other than the current one; in such cases, or when the top -of the stack has been reached, this function returns @code{0} or a -random value. In addition, @code{__builtin_frame_address} may be used +of the stack has been reached, this function returns an unspecified +value. In addition, @code{__builtin_frame_address} may be used to determine if the top of the stack has been reached. Additional post-processing of the returned value may be needed, see @code{__builtin_extract_return_addr}. +The stored representation of the return address in memory may be different +from the address returned by @code{__builtin_return_address}. For example +on AArch64 the stored address may be mangled with return address signing. + Calling this function with a nonzero argument can have unpredictable effects, including crashing the calling program. As a result, calls that are considered unsafe are diagnosed when the @option{-Wframe-address} option is in effect. Such calls should only be made in debugging situations. + +On targets where code addresses are representable as @code{void *}, +@smallexample +void *addr = __builtin_extract_return_addr (__builtin_return_address (0)) +@end smallexample +gives the code address where the current function would return. For example +such address may be used with @code{dladdr} or other interfaces that work +with code addresses. @end deftypefn @deftypefn {Built-in Function} {void *} __builtin_extract_return_addr (void *@var{addr})