diff options
| -rw-r--r-- | gdb/gdbserver/ChangeLog | 5 | ||||
| -rw-r--r-- | gdb/gdbserver/linux-amd64-ipa.c | 52 |
2 files changed, 53 insertions, 4 deletions
diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog index 833075d..ed53648 100644 --- a/gdb/gdbserver/ChangeLog +++ b/gdb/gdbserver/ChangeLog @@ -1,5 +1,10 @@ 2016-08-19 Pedro Alves <palves@redhat.com> + * linux-amd64-ipa.c (alloc_jump_pad_buffer) [__ILP32__]: Try + allocating around 0x80000000. + +2016-08-19 Pedro Alves <palves@redhat.com> + PR gdb/20415 * Makefile.in (x32-linux-ipa.o, x32-avx-linux-ipa.o) (x32-avx512-linux-ipa.o): New rules. diff --git a/gdb/gdbserver/linux-amd64-ipa.c b/gdb/gdbserver/linux-amd64-ipa.c index 15d08ff..0625b85 100644 --- a/gdb/gdbserver/linux-amd64-ipa.c +++ b/gdb/gdbserver/linux-amd64-ipa.c @@ -206,14 +206,57 @@ get_ipa_tdesc (int idx) "unknown ipa tdesc index: %d", idx); } -/* Allocate buffer for the jump pads. Since we're using 32-bit jumps - to reach them, and the executable is at low addresses, MAP_32BIT - works just fine. Shared libraries, being allocated at the top, - are unfortunately out of luck. */ +/* Allocate buffer for the jump pads. The branch instruction has a + reach of +/- 31-bit, and the executable is loaded at low addresses. + + 64-bit: Use MAP_32BIT to allocate in the first 2GB. Shared + libraries, being allocated at the top, are unfortunately out of + luck. + + x32: Since MAP_32BIT is 64-bit only, do the placement manually. + Try allocating at '0x80000000 - SIZE' initially, decreasing until + we hit a free area. This ensures the executable is fully covered, + and is as close as possible to the shared libraries, which are + usually mapped at the top of the first 4GB of the address space. +*/ void * alloc_jump_pad_buffer (size_t size) { +#if __ILP32__ + uintptr_t addr; + int pagesize; + + pagesize = sysconf (_SC_PAGE_SIZE); + if (pagesize == -1) + perror_with_name ("sysconf"); + + addr = 0x80000000 - size; + + /* size should already be page-aligned, but this can't hurt. */ + addr &= ~(pagesize - 1); + + /* Search for a free area. If we hit 0, we're out of luck. */ + for (; addr; addr -= pagesize) + { + void *res; + + /* No MAP_FIXED - we don't want to zap someone's mapping. */ + res = mmap ((void *) addr, size, + PROT_READ | PROT_WRITE | PROT_EXEC, + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + + /* If we got what we wanted, return. */ + if ((uintptr_t) res == addr) + return res; + + /* If we got a mapping, but at a wrong address, undo it. */ + if (res != MAP_FAILED) + munmap (res, size); + } + + return NULL; +#else void *res = mmap (NULL, size, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_PRIVATE | MAP_ANONYMOUS | MAP_32BIT, -1, 0); @@ -221,6 +264,7 @@ alloc_jump_pad_buffer (size_t size) return NULL; return res; +#endif } void |