Date: Mon, 15 Dec 2025 17:00:29 +0000 From: Jessica Clarke <jrtc27@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: 02cb2f8094ba - stable/14 - Revert "rtld: fix allocate_module_tls() variant I fallback to static allocation" Message-ID: <69403ead.e540.47a2d651@gitrepo.freebsd.org>
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The branch stable/14 has been updated by jrtc27: URL: https://cgit.FreeBSD.org/src/commit/?id=02cb2f8094baab0b4299e5fcd1694d9193be14b3 commit 02cb2f8094baab0b4299e5fcd1694d9193be14b3 Author: Jessica Clarke <jrtc27@FreeBSD.org> AuthorDate: 2025-05-28 20:24:52 +0000 Commit: Jessica Clarke <jrtc27@FreeBSD.org> CommitDate: 2025-12-15 16:58:45 +0000 Revert "rtld: fix allocate_module_tls() variant I fallback to static allocation" This was applying a NetBSD fix to FreeBSD. However, the original code was correct for FreeBSD. NetBSD's obj->tlsoffset is relative to the end of the TCB, not the TCB itself, whilst ours is relative to the TCB[1] itself. For example, our allocate_tls uses (char *)tcb + obj->tlsoffset for the memcpy and memset calls. Without this reverted, for dynamically loaded shared objects, Initial Exec accesses to TLS variables on variant I architectures (non-x86) use the correct address, whilst General Dynamic and dlsym(3) use the incorrect address (TLS_TCB_SIZE past the start). Note that, on arm64, LLVM only supports TLSDESC (including LLD) and TLSDESC will use the static resolver if the variable ends up allocated to the static TLS block, even in the presence of dlopen(3), so only dlsym(3) shows the discrepancy there. Whilst here, add a comment to explain this difference to try and avoid the same mistake being made in future. [1] In the case of variant II, it's the amount to subtract, so still positive This reverts commit e9a38ed2fa61fd264a80f24ceb35f39b0ac6463d. Reviewed by: kib (prior version) Fixes: e9a38ed2fa61 ("rtld: fix allocate_module_tls() variant I fallback to static allocation") MFC after: 1 week Differential Revision: https://reviews.freebsd.org/D50565 (cherry picked from commit ccfb1c50e45dbb7fcadf7e1932f63cf1702ef13a) --- libexec/rtld-elf/rtld.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/libexec/rtld-elf/rtld.c b/libexec/rtld-elf/rtld.c index a7fdc153eca8..5117448a0d28 100644 --- a/libexec/rtld-elf/rtld.c +++ b/libexec/rtld-elf/rtld.c @@ -5378,6 +5378,9 @@ get_tls_block_ptr(void *tcb, size_t tcbsize) * it is based on tls_last_offset, and TLS offsets here are really TCB * offsets, whereas libc's tls_static_space is just the executable's static * TLS segment. + * + * NB: This differs from NetBSD's ld.elf_so, where TLS offsets are relative to + * the end of the TCB. */ void * allocate_tls(Obj_Entry *objs, void *oldtcb, size_t tcbsize, size_t tcbalign) @@ -5612,7 +5615,7 @@ allocate_module_tls(int index) if (obj->tls_static) { #ifdef TLS_VARIANT_I - p = (char *)_tcb_get() + obj->tlsoffset + TLS_TCB_SIZE; + p = (char *)_tcb_get() + obj->tlsoffset; #else p = (char *)_tcb_get() - obj->tlsoffset; #endifhelp
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