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Diffstat (limited to 'gdb/doc/gdb.texinfo')
| -rw-r--r-- | gdb/doc/gdb.texinfo | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo index f17c800..0cadc96 100644 --- a/gdb/doc/gdb.texinfo +++ b/gdb/doc/gdb.texinfo @@ -10378,6 +10378,23 @@ message. @value{GDBN} handles arguments to @code{ftrace} exactly as for @code{trace}. +On 32-bit x86-architecture systems, fast tracepoints normally need to +be placed at an instruction that is 5 bytes or longer, but can be +placed at 4-byte instructions if the low 64K of memory of the target +program is available to install trampolines. Some Unix-type systems, +such as @sc{gnu}/Linux, exclude low addresses from the program's +address space; but for instance with the Linux kernel it is possible +to let @value{GDBN} use this area by doing a @command{sysctl} command +to set the @code{mmap_min_addr} kernel parameter, as in + +@example +sudo sysctl -w vm.mmap_min_addr=32768 +@end example + +@noindent +which sets the low address to 32K, which leaves plenty of room for +trampolines. The minimum address should be set to a page boundary. + @item strace @var{location} [ if @var{cond} ] @cindex set static tracepoint @cindex static tracepoints, setting @@ -34915,6 +34932,8 @@ encoded). @value{GDBN} will continue to supply the values of symbols @itemx qTfP @itemx qTfV @itemx QTFrame +@itemx qTMinFTPILen + @xref{Tracepoint Packets}. @item qThreadExtraInfo,@var{thread-id} @@ -35438,6 +35457,30 @@ numbers. Like @samp{QTFrame:range:@var{start}:@var{end}}, but select the first frame @emph{outside} the given range of addresses (exclusive). +@item qTMinFTPILen +This packet requests the minimum length of instruction at which a fast +tracepoint (@pxref{Set Tracepoints}) may be placed. For instance, on +the 32-bit x86 architecture, it is possible to use a 4-byte jump, but +it depends on the target system being able to create trampolines in +the first 64K of memory, which might or might not be possible for that +system. So the reply to this packet will be 4 if it is able to +arrange for that. + +Replies: + +@table @samp +@item 0 +The minimum instruction length is currently unknown. +@item @var{length} +The minimum instruction length is @var{length}, where @var{length} is greater +or equal to 1. @var{length} is a hexadecimal number. A reply of 1 means +that a fast tracepoint may be placed on any instruction regardless of size. +@item E +An error has occurred. +@item +An empty reply indicates that the request is not supported by the stub. +@end table + @item QTStart Begin the tracepoint experiment. Begin collecting data from tracepoint hits in the trace frame buffer. This packet supports the |