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authorPedro Alves <palves@redhat.com>2016-08-19 12:07:45 +0100
committerPedro Alves <palves@redhat.com>2016-08-19 12:11:30 +0100
commit9c235a72a112c5656f17499c0c0d3ad73609833d (patch)
treebcbc1378ccf3e5264badee159d0ac1eef508973d /gdb
parent201506dadd117df72d0528f735e44ce2e68cc66f (diff)
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x32 Fast tracepoints: Customize jump pad address
MAP_32BIT is ignored on x32, meaning the jump pad can end up somewhere between 2GB and 4GB, too far away from the executable for 5-byte relative jumps (JMP rel32). So on x32, try explicitly placing the jump pad near the middle of the available address space. gdb/gdbserver/ChangeLog: 2016-08-19 Pedro Alves <palves@redhat.com> * linux-amd64-ipa.c (alloc_jump_pad_buffer) [__ILP32__]: Try allocating around 0x80000000.
Diffstat (limited to 'gdb')
-rw-r--r--gdb/gdbserver/ChangeLog5
-rw-r--r--gdb/gdbserver/linux-amd64-ipa.c52
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