diff options
Diffstat (limited to 'gdb/i386-tdep.c')
| -rw-r--r-- | gdb/i386-tdep.c | 45 |
1 files changed, 33 insertions, 12 deletions
diff --git a/gdb/i386-tdep.c b/gdb/i386-tdep.c index 2f0b6f5e929..a4e3a220554 100644 --- a/gdb/i386-tdep.c +++ b/gdb/i386-tdep.c @@ -7109,10 +7109,12 @@ static const int i386_record_regmap[] = }; /* Check that the given address appears suitable for a fast - tracepoint, which on x86 means that we need an instruction of at + tracepoint, which on x86-64 means that we need an instruction of at least 5 bytes, so that we can overwrite it with a 4-byte-offset jump and not have to worry about program jumps to an address in the - middle of the tracepoint jump. Returns 1 if OK, and writes a size + middle of the tracepoint jump. On x86, it may be possible to use + 4-byte jumps with a 2-byte offset to a trampoline located in the + bottom 64 KiB of memory. Returns 1 if OK, and writes a size of instruction to replace, and 0 if not, plus an explanatory string. */ @@ -7123,10 +7125,26 @@ i386_fast_tracepoint_valid_at (struct gdbarch *gdbarch, int len, jumplen; static struct ui_file *gdb_null = NULL; - /* This is based on the target agent using a 4-byte relative jump. - Alternate future possibilities include 8-byte offset for x86-84, - or 3-byte jumps if the program has trampoline space close by. */ - jumplen = 5; + /* Ask the target for the minimum instruction length supported. */ + jumplen = target_get_min_fast_tracepoint_insn_len (); + + if (jumplen < 0) + { + /* If the target does not support the get_min_fast_tracepoint_insn_len + operation, assume that fast tracepoints will always be implemented + using 4-byte relative jumps on both x86 and x86-64. */ + jumplen = 5; + } + else if (jumplen == 0) + { + /* If the target does support get_min_fast_tracepoint_insn_len but + returns zero, then the IPA has not loaded yet. In this case, + we optimistically assume that truncated 2-byte relative jumps + will be available on x86, and compensate later if this assumption + turns out to be incorrect. On x86-64 architectures, 4-byte relative + jumps will always be used. */ + jumplen = (register_size (gdbarch, 0) == 8) ? 5 : 4; + } /* Dummy file descriptor for the disassembler. */ if (!gdb_null) @@ -7134,6 +7152,9 @@ i386_fast_tracepoint_valid_at (struct gdbarch *gdbarch, /* Check for fit. */ len = gdb_print_insn (gdbarch, addr, gdb_null, NULL); + if (isize) + *isize = len; + if (len < jumplen) { /* Return a bit of target-specific detail to add to the caller's @@ -7144,12 +7165,12 @@ i386_fast_tracepoint_valid_at (struct gdbarch *gdbarch, len, jumplen); return 0; } - - if (isize) - *isize = len; - if (msg) - *msg = NULL; - return 1; + else + { + if (msg) + *msg = NULL; + return 1; + } } static int |