Message ID | Ye4hVIPjYpPZxj5j@squeak.grove.modra.org |
---|---|
State | New |
Headers | show |
Series | [PowerPC64] Use medium model toc accesses throughout | expand |
On 1/23/22 9:47 PM, Alan Modra via Libc-alpha wrote: > On Sun, Jan 23, 2022 at 11:12:13PM +1030, Alan Modra wrote: >> There's a serious problem in libgcc too. libgcc ifuncs access the >> AT_HWCAP words stored in the tcb with an offset from the thread >> pointer (r13), but r13 isn't set at the time _dl_relocate_static_pie >> runs, and I'm loathe to try calling init_tls early. A better approach >> that might work is to fake r13 so that _dl_hwcap is at the expected >> offset where we'd normally find the tcb hwcap words. > > Like this. > > libgcc ifunc resolvers that access hwcap via a field in the tcb can't > be called until the thread pointer is set up. This patch sets up a > fake thread pointer early so that static-pies won't segfault on > attempting to relocate themselves. > I suspect the thread pointer needs to be setup more. How much, I am not sure. Looking into the failure of tst-tlsifunc-static, we would need similar access to at_platform when resolving ifunc for similar reasons of hwcap. That seems like an easy fix. However, I am not sure what to make of the other failure in this test. A pointer into tls is created as part of running an ifunc resolver. Do we need to preserve that behavior?
On Wed, Feb 16, 2022 at 05:02:51PM -0600, Paul E Murphy wrote: > > > On 1/23/22 9:47 PM, Alan Modra via Libc-alpha wrote: > > On Sun, Jan 23, 2022 at 11:12:13PM +1030, Alan Modra wrote: > > > There's a serious problem in libgcc too. libgcc ifuncs access the > > > AT_HWCAP words stored in the tcb with an offset from the thread > > > pointer (r13), but r13 isn't set at the time _dl_relocate_static_pie > > > runs, and I'm loathe to try calling init_tls early. A better approach > > > that might work is to fake r13 so that _dl_hwcap is at the expected > > > offset where we'd normally find the tcb hwcap words. > > > > Like this. > > > > libgcc ifunc resolvers that access hwcap via a field in the tcb can't > > be called until the thread pointer is set up. This patch sets up a > > fake thread pointer early so that static-pies won't segfault on > > attempting to relocate themselves. > > > > I suspect the thread pointer needs to be setup more. How much, I am not > sure. > > Looking into the failure of tst-tlsifunc-static, we would need similar > access to at_platform when resolving ifunc for similar reasons of hwcap. > That seems like an easy fix. Yes, it means arranging to have a copy of at_platform accessible from the fake tls pointer reg, not just __tcb_hwcap. A tcbhead_t in sysdeps/powerpc/hwcapinfo.c replacing __tcb_hwcap and __tcb_platform there would be best, I think. > However, I am not sure what to make of the other failure in this test. A > pointer into tls is created as part of running an ifunc resolver. Do we > need to preserve that behavior? Tulio will be better placed to answer this question. Note that a number of glibc test failures disappear with binutils commit 3a3a4c1fe4c.
diff --git a/sysdeps/powerpc/powerpc64/dl-machine.h b/sysdeps/powerpc/powerpc64/dl-machine.h index eb41c85280..413bbe7c06 100644 --- a/sysdeps/powerpc/powerpc64/dl-machine.h +++ b/sysdeps/powerpc/powerpc64/dl-machine.h @@ -589,6 +589,27 @@ elf_machine_plt_value (struct link_map *map, const Elf64_Rela *reloc, #define ARCH_LA_PLTEXIT ppc64v2_gnu_pltexit #endif +#if ENABLE_STATIC_PIE && !defined SHARED && !IS_IN (rtld) +#include <libc-diag.h> +#include <tcb-offsets.h> + +/* Set up r13 for _dl_relocate_static_pie so that libgcc ifuncs that + normally access the tcb copy of hwcap will see __tcb_hwcap. */ + +static inline void __attribute__ ((always_inline)) +ppc_init_fake_thread_pointer (void) +{ + DIAG_PUSH_NEEDS_COMMENT; + /* We are playing pointer tricks. Silence gcc warning. */ + DIAG_IGNORE_NEEDS_COMMENT (4.9, "-Warray-bounds"); + __thread_register = (char *) &__tcb_hwcap - TCB_HWCAP; + DIAG_POP_NEEDS_COMMENT; +} + +#define ELF_MACHINE_BEFORE_RTLD_RELOC(map, dynamic_info) \ + ppc_init_fake_thread_pointer (); +#endif /* ENABLE_STATIC_PIE && !defined SHARED && !IS_IN (rtld) */ + #endif /* dl_machine_h */ #ifdef RESOLVE_MAP