[PATCH v2] nptl: use mmap to allocate initial TLS data for static PIE on noMMU - devel

6 Sep 2022

Static PIE ELFs may be loaded on noMMU linux platforms with FDPIC
support, but they don't have adjustable brk, and thus cannot allocate
memory for the TLS. Use mmap instead of sbrk to allocate initial TLS
memory when building with static PIE support for noMMU.
Signed-off-by: Max Filippov jcmvbkbc@gmail.com
---
Change v1->v2:
- fix typo and add clarification in comment
libpthread/nptl/sysdeps/generic/libc-tls.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/libpthread/nptl/sysdeps/generic/libc-tls.c b/libpthread/nptl/sysdeps/generic/libc-tls.c
index d9c09fdd6667..7cfe9ac1a85c 100644
--- a/libpthread/nptl/sysdeps/generic/libc-tls.c
+++ b/libpthread/nptl/sysdeps/generic/libc-tls.c
@@ -169,10 +169,13 @@ __libc_setup_tls (size_t tcbsize, size_t tcbalign)
      for FDPIC MMU-less platforms:
      fs/binfmt_elf_fdpic.c: fix brk area overlap with stack on NOMMU
      https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/fs/bi...
+     Loading static PIE ELFs on noMMU is possible since the linux kernel commit
+     1bde925d2354 ("fs/binfmt_elf_fdpic.c: provide NOMMU loader for regular ELF binaries")
+     and it is subject to the same brk restriction.
    */
 # if defined(TLS_TCB_AT_TP)
   tcb_offset = roundup (memsz + GL(dl_tls_static_size), tcbalign);
-#  if defined(__FDPIC__)
+#  if defined(__FDPIC__) || (!defined(__ARCH_USE_MMU__) && defined(STATIC_PIE))
   tlsblock = mmap (NULL, tcb_offset + tcbsize + max_align,
                    PROT_READ|PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 #  else
@@ -180,7 +183,7 @@ __libc_setup_tls (size_t tcbsize, size_t tcbalign)
 #  endif
 # elif defined(TLS_DTV_AT_TP)
   tcb_offset = roundup (tcbsize, align ?: 1);
-#  if defined(__FDPIC__)
+#  if defined(__FDPIC__) || (!defined(__ARCH_USE_MMU__) && defined(STATIC_PIE))
   tlsblock = mmap (NULL, tcb_offset + memsz + max_align + TLS_PRE_TCB_SIZE + GL(dl_tls_static_size),
                    PROT_READ|PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 #  else
-- 
2.30.2


    