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gdb, gdbserver: introduce the 'x' RSP packet for binary memory read

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Introduce an RSP packet, 'x', for reading from the remote server
memory in binary format.  The binary write packet, 'X' already exists.
The 'x' packet is essentially the same as 'm', except that the
returned data is in binary format.  For transferring relatively large
data from the memory of the remote process, the 'x' packet can reduce the
transfer costs.

For example, without this patch, fetching ~100MB of data from a remote
target takes

  (gdb) dump binary memory temp.o 0x00007f3ba4c576c0 0x00007f3bab709400
  2024-03-13 16:17:42.626 - command started
  2024-03-13 16:18:24.151 - command finished
  Command execution time: 32.136785 (cpu), 41.525515 (wall)
  (gdb)

whereas with this patch, we obtain

  (gdb) dump binary memory temp.o 0x00007fec39fce6c0 0x00007fec40a80400
  2024-03-13 16:20:48.609 - command started
  2024-03-13 16:21:16.873 - command finished
  Command execution time: 20.447970 (cpu), 28.264202 (wall)
  (gdb)

We see improvements not only when reading bulk data as above, but also
when making a large number of small memory access requests.

For example, without this patch:

  (gdb) pipe x/100000xw $pc | wc -l
  2024-03-13 16:04:57.112 - command started
  25000
  2024-03-13 16:05:10.798 - command finished
  Command execution time: 9.952364 (cpu), 13.686581 (wall)

With this patch:

  (gdb) pipe x/100000xw $pc | wc -l
  2024-03-13 16:06:48.160 - command started
  25000
  2024-03-13 16:06:57.750 - command finished
  Command execution time: 6.541425 (cpu), 9.589839 (wall)
  (gdb)

Another example, where we create a core file of a GDB process.

  (gdb) gcore /tmp/core.1
  ...
  Command execution time: 85.496967 (cpu), 133.224373 (wall)

vs.

  (gdb) gcore /tmp/core.1
  ...
  Command execution time: 48.328885 (cpu), 115.032289 (wall)

Regression-tested on X86-64 using the unix (default) and
native-extended-gdbserver board files.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>
Approved-By: Tom Tromey <tom@tromey.com>
This commit is contained in:
Tankut Baris Aktemur
2024-12-19 12:31:50 +01:00
parent 792b26bb0c
commit e16e6389a7
6 changed files with 217 additions and 21 deletions
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2
gdbserver/remote-utils.h
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@@ -57,6 +57,8 @@ void decode_m_packet (const char *from, CORE_ADDR * mem_addr_ptr,
unsigned int *len_ptr);
void decode_M_packet (const char *from, CORE_ADDR * mem_addr_ptr,
unsigned int *len_ptr, unsigned char **to_p);
void decode_x_packet (const char *from, CORE_ADDR *mem_addr_ptr,
unsigned int *len_ptr);
int decode_X_packet (char *from, int packet_len, CORE_ADDR * mem_addr_ptr,
unsigned int *len_ptr, unsigned char **to_p);
int decode_xfer_write (char *buf, int packet_len,