https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85990
--- Comment #2 from hjl at gcc dot gnu.org <hjl at gcc dot gnu.org> --- Author: hjl Date: Tue Jun 12 15:35:22 2018 New Revision: 261501 URL: https://gcc.gnu.org/viewcvs?rev=261501&root=gcc&view=rev Log: Linux/x86: Update TARGET_THREAD_SPLIT_STACK_OFFSET comments Glibc 2.18 was changed by commit ecbf434213c0333d81706074e4d107ac45011635 Author: Andreas Jaeger <a...@suse.de> Date: Wed May 15 20:20:54 2013 +0200 Reserve new TLS field for x86 and x86_64 [BZ #10686] * sysdeps/x86_64/tls.h (struct tcbhead_t): Add __private_ss field. * sysdeps/i386/tls.h (struct tcbhead_t): Likewise. to reduce the size of __private_tm to make room for __private_ss, which was supposed to be used for TARGET_THREAD_SPLIT_STACK_OFFSET: typedef struct { void *tcb; /* Pointer to the TCB. Not necessarily the thread descriptor used by libpthread. */ dtv_t *dtv; void *self; /* Pointer to the thread descriptor. */ int multiple_threads; uintptr_t sysinfo; uintptr_t stack_guard; uintptr_t pointer_guard; int gscope_flag; int __glibc_reserved1; /* Reservation of some values for the TM ABI. */ void *__private_tm[4]; /* GCC split stack support. */ void *__private_ss; } tcbhead_t; But the offset of __private_ss for i386 was mistakenly set to 0x30, instead of 0x34 and libgcc/config/i386/morestack.S has: cmpl %gs:0x30,%eax # See if we have enough space. movl %eax,%gs:0x30 # Save the new stack boundary. movl %eax,%gs:0x30 # Save the new stack boundary. movl %ecx,%gs:0x30 # Save new stack boundary. movl %eax,%gs:0x30 movl %gs:0x30,%eax movl %eax,%gs:0x30 Since update TARGET_THREAD_SPLIT_STACK_OFFSET changes split stack ABI, glibc 2.28 has been changed by commit 0221ce2a90be2d40fc90f0b5dcec77a1ec013f53 Author: H.J. Lu <hjl.to...@gmail.com> Date: Tue Jun 12 06:23:28 2018 -0700 i386: Change offset of __private_ss to 0x30 [BZ #23250] to match GCC: typedef struct { void *tcb; /* Pointer to the TCB. Not necessarily the thread descriptor used by libpthread. */ dtv_t *dtv; void *self; /* Pointer to the thread descriptor. */ int multiple_threads; uintptr_t sysinfo; uintptr_t stack_guard; uintptr_t pointer_guard; int gscope_flag; int __glibc_reserved1; /* Reservation of some values for the TM ABI. */ void *__private_tm[3]; /* GCC split stack support. */ void *__private_ss; void *__glibc_reserved2; } tcbhead_t; PR target/85990 * config/i386/gnu-user.h (TARGET_THREAD_SPLIT_STACK_OFFSET): Update comments. * config/i386/gnu-user64.h (TARGET_THREAD_SPLIT_STACK_OFFSET): Likewise. Modified: trunk/gcc/ChangeLog trunk/gcc/config/i386/gnu-user.h trunk/gcc/config/i386/gnu-user64.h
