Date: Sun, 5 Nov 2017 13:30:53 +0100 From: Szabolcs Nagy <nsz@...t70.net> To: musl@...ts.openwall.com Subject: Re: SIGSEGV_FAULT_STACKPOINTER on powerpc * Tobias Koch <tobias.koch@...terra.com> [2017-11-05 11:28:08 +0000]: > > libsigsegv defines SIGSEGV_FAULT_STACKPOINTER in fault-linux-powerpc.h as > > # define SIGSEGV_FAULT_STACKPOINTER ((ucontext_t *) ucp)->uc_mcontext.regs->gpr > > which doesn't match up with what's defined in musl's arch/powerpc/bits/signal.h. I took a guess and changed it to > > # define SIGSEGV_FAULT_STACKPOINTER ((ucontext_t *) ucp)->uc_mcontext.gregs > > to make it compile, but I don't know if that is correct. I'd appreciate any help. > in glibc uc_mcontext member of ucontext_t is an union of pt_regs* (linux ptrace.h defines it) and mcontext_t* (same as in musl). but the standard requires mcontext_t there, not an union of pointers, so the powerpc linux abi is broken. to access gpregs in glibc you can use either of (pt_regs*) ucp->uc_mcontext.regs (mcontext_t*) ucp->uc_mcontext.uc_regs in musl it's (mcontext_t*) ucp->uc_regs the pointers may point to the tail of the ucontext_t struct where musl has its ucp->uc_mcontext field with the right type, but i don't know if that's guaranteed. so the standard conform way (using ucp->uc_mcontext) to access the registers is not reliable. you can try to use the non-standard uc_regs pointer: #ifdef __GLIBC__ #define uc_regs uc_mcontext.uc_regs #endif #define SIGSEGV_FAULT_STACKPOINTER ((ucontext_t *) ucp)->uc_regs->gregs
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