On 2023/8/8 17:55, Jiajie Chen wrote:
On 2023/8/8 14:10, bibo mao wrote:
I am not familiar with gdb, is there abi breakage?
I do not know how gdb client works with gdb server with different versions.
There seemed no versioning in the process, but rather in-code xml
validation. In gdb, the code only allows new xml (fcc0-7) and
rejects old one (fcc), so gdb breaks qemu first and do not consider
backward compatibility with qemu.
Not abi breakage, but gdb will complain:
warning: while parsing target description (at line 1): Target
description specified unknown architecture "loongarch64"
warning: Could not load XML target description; ignoring
warning: No executable has been specified and target does not support
determining executable automatically. Try using the "file" command.
Truncated register 38 in remote 'g' packet
Sorry, to be clear, the actual error message is:
(gdb) target extended-remote localhost:1234
Remote debugging using localhost:1234
warning: Architecture rejected target-supplied description
warning: No executable has been specified and target does not support
It rejects the target description xml given by qemu, thus using the
builtin one. However, there is a mismatch in fcc registers, so it
will not work if we list floating point registers.
At the same time, if we are using loongarch32 target(I recently
posted patches to support this), it will reject the target
description and fallback to loongarch64, making gcc not usable.
And gdb can no longer debug kernel running in qemu. You can
reproduce this error using latest qemu(without this patch) and
gdb(13.1 or later).
Regards
Bibo Mao
在 2023/8/8 13:42, Jiajie Chen 写道:
Since GDB 13.1(GDB commit ea3352172), GDB LoongArch changed to use
fcc0-7 instead of fcc register. This commit partially reverts commit
2f149c759 (`target/loongarch: Update gdb_set_fpu() and gdb_get_fpu()`)
to match the behavior of GDB.
Note that it is a breaking change for GDB 13.0 or earlier, but it is
also required for GDB 13.1 or later to work.
Signed-off-by: Jiajie Chen <c@jia.je>
---
gdb-xml/loongarch-fpu.xml | 9 ++++++++-
target/loongarch/gdbstub.c | 16 +++++++---------
2 files changed, 15 insertions(+), 10 deletions(-)
diff --git a/gdb-xml/loongarch-fpu.xml b/gdb-xml/loongarch-fpu.xml
index 78e42cf5dd..e81e3382e7 100644
--- a/gdb-xml/loongarch-fpu.xml
+++ b/gdb-xml/loongarch-fpu.xml
@@ -45,6 +45,13 @@
<reg name="f29" bitsize="64" type="fputype" group="float"/>
<reg name="f30" bitsize="64" type="fputype" group="float"/>
<reg name="f31" bitsize="64" type="fputype" group="float"/>
- <reg name="fcc" bitsize="64" type="uint64" group="float"/>
+ <reg name="fcc0" bitsize="8" type="uint8" group="float"/>
+ <reg name="fcc1" bitsize="8" type="uint8" group="float"/>
+ <reg name="fcc2" bitsize="8" type="uint8" group="float"/>
+ <reg name="fcc3" bitsize="8" type="uint8" group="float"/>
+ <reg name="fcc4" bitsize="8" type="uint8" group="float"/>
+ <reg name="fcc5" bitsize="8" type="uint8" group="float"/>
+ <reg name="fcc6" bitsize="8" type="uint8" group="float"/>
+ <reg name="fcc7" bitsize="8" type="uint8" group="float"/>
<reg name="fcsr" bitsize="32" type="uint32" group="float"/>
</feature>
diff --git a/target/loongarch/gdbstub.c b/target/loongarch/gdbstub.c
index 0752fff924..15ad6778f1 100644
--- a/target/loongarch/gdbstub.c
+++ b/target/loongarch/gdbstub.c
@@ -70,10 +70,9 @@ static int loongarch_gdb_get_fpu(CPULoongArchState *env,
{
if (0 <= n && n < 32) {
return gdb_get_reg64(mem_buf, env->fpr[n].vreg.D(0));
- } else if (n == 32) {
- uint64_t val = read_fcc(env);
- return gdb_get_reg64(mem_buf, val);
- } else if (n == 33) {
+ } else if (32 <= n && n < 40) {
+ return gdb_get_reg8(mem_buf, env->cf[n - 32]);
+ } else if (n == 40) {
return gdb_get_reg32(mem_buf, env->fcsr0);
}
return 0;
@@ -87,11 +86,10 @@ static int loongarch_gdb_set_fpu(CPULoongArchState *env,
if (0 <= n && n < 32) {
env->fpr[n].vreg.D(0) = ldq_p(mem_buf);
length = 8;
- } else if (n == 32) {
- uint64_t val = ldq_p(mem_buf);
- write_fcc(env, val);
- length = 8;
- } else if (n == 33) {
+ } else if (32 <= n && n < 40) {
+ env->cf[n - 32] = ldub_p(mem_buf);
+ length = 1;
+ } else if (n == 40) {
env->fcsr0 = ldl_p(mem_buf);
length = 4;
}