From 30e32da6aafcef5a5d5a1c91e233636db6493fc8 Mon Sep 17 00:00:00 2001 From: Florian Weimer Date: Thu, 2 Jan 2025 13:45:27 +0100 Subject: [PATCH] elf: Use TLS_DTV_OFFSET in __tls_get_addr This fixes commit 5e249192cac7354af02a7347a0d8c984e0c88ed3 ("elf: Remove the GET_ADDR_ARGS and related macros from the TLS code"): GET_ADDR_ARGS was indeed unused, but GET_ADDR_OFFSET was used on several targets, those that define TLS_DTV_OFFSET. Instead of reintroducing GET_ADDR_OFFSET, use TLS_DTV_OFFSET directly, now that it is defined on all targets. In the new tls_get_addr_adjust helper function, add a cast to uintptr_t to help the s390 case, where the offset can be positive or negative, depending on the addresses malloc returns. The cast avoids pointer wraparound/overflow. The outer uintptr_t cast is needed to suppress a warning on x86-64 x32 about mismatched integer/pointer sizes. Eventually this offset should be folded into the DTV addresses themselves, to eliminate the subtraction on the TLS fast path. This will require an adjustment to libthread_db because the debugger interface currently returns unadjusted pointers. Reviewed-by: Adhemerval Zanella --- elf/dl-tls.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/elf/dl-tls.c b/elf/dl-tls.c index bcb5250c82..c2d17265fb 100644 --- a/elf/dl-tls.c +++ b/elf/dl-tls.c @@ -890,6 +890,18 @@ _dl_update_slotinfo (unsigned long int req_modid, size_t new_gen) return the_map; } +/* Adjust the TLS variable pointer using the TLS descriptor offset and + the ABI-specific offset. */ +static inline void * +tls_get_addr_adjust (void *from_dtv, tls_index *ti) +{ + /* Perform arithmetic in uintptr_t to avoid pointer wraparound + issues. The outer cast to uintptr_t suppresses a warning about + pointer/integer size mismatch on ILP32 targets with 64-bit + ti_offset. */ + return (void *) (uintptr_t) ((uintptr_t) from_dtv + ti->ti_offset + + TLS_DTV_OFFSET); +} static void * __attribute_noinline__ @@ -939,7 +951,7 @@ tls_get_addr_tail (tls_index *ti, dtv_t *dtv, struct link_map *the_map) dtv[ti->ti_module].pointer.to_free = NULL; dtv[ti->ti_module].pointer.val = p; - return (char *) p + ti->ti_offset; + return tls_get_addr_adjust (p, ti); } else __rtld_lock_unlock_recursive (GL(dl_load_tls_lock)); @@ -948,7 +960,7 @@ tls_get_addr_tail (tls_index *ti, dtv_t *dtv, struct link_map *the_map) dtv[ti->ti_module].pointer = result; assert (result.to_free != NULL); - return (char *) result.val + ti->ti_offset; + return tls_get_addr_adjust (result.val, ti); } @@ -964,7 +976,7 @@ update_get_addr (tls_index *ti, size_t gen) if (__glibc_unlikely (p == TLS_DTV_UNALLOCATED)) return tls_get_addr_tail (ti, dtv, the_map); - return (void *) p + ti->ti_offset; + return tls_get_addr_adjust (p, ti); } /* For all machines that have a non-macro version of __tls_get_addr, we @@ -1015,7 +1027,7 @@ __tls_get_addr (tls_index *ti) if (__glibc_unlikely (p == TLS_DTV_UNALLOCATED)) return tls_get_addr_tail (ti, dtv, NULL); - return (char *) p + ti->ti_offset; + return tls_get_addr_adjust (p, ti); } #endif /* SHARED */