https://wiki.osdev.org/QEMU_and_GDB_in_long_mode
The patch offered there works for latest GDB (8.2.1) with a very slight modification:
Code: Select all
--- gdb/remote.c 2019-04-25 00:49:04.238196076 +0300
+++ gdb/remote.c 2019-04-25 00:49:08.038221311 +0300
@@ -8035,8 +8035,23 @@
/* Further sanity checks, with knowledge of the architecture. */
if (buf_len > 2 * rsa->sizeof_g_packet)
- error (_("Remote 'g' packet reply is too long (expected %ld bytes, got %d "
- "bytes): %s"), rsa->sizeof_g_packet, buf_len / 2, rs->buf);
+ {
+ warning (_("Assuming long-mode change. [Remote 'g' packet reply is too long: %s]"), rs->buf);
+ rsa->sizeof_g_packet = buf_len ;
+ for (i = 0; i < gdbarch_num_regs (gdbarch); i++)
+ {
+ if (rsa->regs[i].pnum == -1)
+ continue;
+ if (rsa->regs[i].offset >= rsa->sizeof_g_packet)
+ rsa->regs[i].in_g_packet = 0;
+ else
+ rsa->regs[i].in_g_packet = 1;
+ }
+
+ // HACKFIX: Make sure at least the lower half of EIP is set correctly, so the proper
+ // breakpoint is recognized (and triggered).
+ rsa->regs[8].offset = 16*8;
+ }
/* Save the size of the packet sent to us by the target. It is used
as a heuristic when determining the max size of packets that the
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cd gdb/gdb-8.2.1
patch -p0 < gdb-longmode.patch