"Jonathan S. Shapiro" <[EMAIL PROTECTED]> writes: > On Fri, 2007-08-03 at 11:06 -0400, Daniel Jacobowitz wrote: > > crtbeginT.o is used for -static; crtbegin.o is used without -static. > > I don't recall why they have to be different. > > So far as we can tell from looking at the linux versions, the only > difference is that crtbeginT is calling > > register_frame_info_bases > deregister_frame_info_bases > > I suspect that these are related to the exception frame walker, because > if --static (therefore crtbeginT) is provided then --eh-frame-header is > not applied by default. That is: I suspect that --static does not > support exception frame walking. This smells like a Linux legacy issue > that may not apply to us. Can anybody confirm or correct that guess?
If you pass --eh-frame-header to the linker, it will create a PT_GNU_EH_FRAME segment in the output file. The code in gcc/unwind-dw2-fde-glibc.c will locate that segment by using dl_iterate_phdr. dl_iterate_phdr is provided by glibc. At one time it only worked for dynamically linked binaries, but I believe that it currently also works for statically linked binaries. So I believe that in principle it would now be possible to use --eh-frame-header and unwind-dw2-fde-glibc.c with statically linked binaries. But I haven't actually tried. In order for you to use --eh-frame-header, your libc will need to provide dl_iterate_phdr. The advantage of this approach is that it does not require registering the exceptions at program start time, thus saving a bit of startup time. Also, if everything works correctly, the linker will create a sorted list of FDEs, which will permit faster lookup of the required stack unwinding information when an exception occurs. If you don't have dl_iterate_phdr, then you will need to call register_frame_info_bases at startup time. And you won't want to use --eh-frame-header. All of this is completely ELF specific, by the way. Ian
