On 03/30/2012 08:26 PM, Ian Lance Taylor wrote: > Oliver Kowalke <oliver.kowalke@xxxxxx> writes: > >> Am 30.03.2012 17:08, schrieb Ian Lance Taylor: >>> "Oliver Kowalke"<oliver.kowalke@xxxxxx> writes: >>> >>>> I get a segfault with following app - could you verify this? >>> This program works fine for me (gcc 4.4.3, glibc 2.11.1, Ubuntu Lucid) >>> in 64-bit mode. But now I see that you are using 32-bit mode. I can >>> confirm that the program crashes for me in that mode. >>> >>> Looking at the 32-bit implementation of makecontext in glibc, I can see >>> that the problem is that it doesn't set up correct unwind information >>> for the parameters pushed on the stack. The effect is that the first >>> parameter on the stack appears to be a PC value. I think this is a bug >>> in glibc. It should be possible to arrange for unwind information which >>> skips %ebx words on the stack. >> >> I think the test app is not correct - on ppc32/linux it never returns. > > Any application that tries to walk up the stack to the end is > unfortunately going to be tricky and non-portable. If you want a > portable program you should always have some way to stop the stack > unwind yourself. That is unfortunate but true. I'm not at all happy about that. Any system that supports backtrace() should be able to get this right. I've had to fix more than one system to make unwinding work right; if it doesn't, that can (and IMO should) be treated as a bug. Andrew.
