[PATCH v7 10/18] [gdb/aarch64] sme: Signal frame support

Luis Machado via Gdb-patches
2023-09-18T21:29:27Z

Teach gdb about the ZA/SSVE state on signal frames and how to restore
the contents of the registers.

There is a new ZA_MAGIC context that the Linux Kernel uses to communicate
the ZA register state to gdb.

The SVE_MAGIC context has also been adjusted to contain a flag indicating
whether it is a SVE or SSVE state.

Regression-tested on aarch64-linux Ubuntu 22.04/20.04.

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
---
gdb/aarch64-linux-tdep.c | 88 +++++++++++++++++++--
gdb/nat/aarch64-scalable-linux-sigcontext.h | 5 +-
2 files changed, 84 insertions(+), 9 deletions(-)

diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
index bdd5cb05c10..f76d1888072 100644
--- a/gdb/aarch64-linux-tdep.c
+++ b/gdb/aarch64-linux-tdep.c
@@ -48,6 +48,7 @@
#include "linux-record.h"

#include "arch/aarch64-mte-linux.h"
+#include "arch/aarch64-scalable-linux.h"

#include "arch-utils.h"
#include "value.h"
@@ -152,6 +153,7 @@
#define AARCH64_EXTRA_MAGIC 0x45585401
#define AARCH64_FPSIMD_MAGIC 0x46508001
#define AARCH64_SVE_MAGIC 0x53564501
+#define AARCH64_ZA_MAGIC 0x54366345

/* Defines for the extra_context that follows an AARCH64_EXTRA_MAGIC. */
#define AARCH64_EXTRA_DATAP_OFFSET 8
@@ -164,13 +166,23 @@

/* Defines for the sve structure that follows an AARCH64_SVE_MAGIC. */
#define AARCH64_SVE_CONTEXT_VL_OFFSET 8
+#define AARCH64_SVE_CONTEXT_FLAGS_OFFSET 10
#define AARCH64_SVE_CONTEXT_REGS_OFFSET 16
#define AARCH64_SVE_CONTEXT_P_REGS_OFFSET(vq) (32 * vq * 16)
#define AARCH64_SVE_CONTEXT_FFR_OFFSET(vq) \
(AARCH64_SVE_CONTEXT_P_REGS_OFFSET (vq) + (16 * vq * 2))
#define AARCH64_SVE_CONTEXT_SIZE(vq) \
(AARCH64_SVE_CONTEXT_FFR_OFFSET (vq) + (vq * 2))
+/* Flag indicating the SVE Context describes streaming mode. */
+#define SVE_SIG_FLAG_SM 0x1

+/* SME constants. */
+#define AARCH64_SME_CONTEXT_SVL_OFFSET 8
+#define AARCH64_SME_CONTEXT_REGS_OFFSET 16
+#define AARCH64_SME_CONTEXT_ZA_SIZE(svq) \
+ ((sve_vl_from_vq (svq) * sve_vl_from_vq (svq)))
+#define AARCH64_SME_CONTEXT_SIZE(svq) \
+ (AARCH64_SME_CONTEXT_REGS_OFFSET + AARCH64_SME_CONTEXT_ZA_SIZE (svq))

/* Read an aarch64_ctx, returning the magic value, and setting *SIZE to the
size, or return 0 on error. */
@@ -324,7 +336,10 @@ aarch64_linux_sigframe_init (const struct tramp_frame *self,
CORE_ADDR section_end = section + AARCH64_SIGCONTEXT_RESERVED_SIZE;
CORE_ADDR fpsimd = 0;
CORE_ADDR sve_regs = 0;
+ CORE_ADDR za_state = 0;
+ uint64_t svcr = 0;
uint32_t size, magic;
+ size_t vq = 0, svq = 0;
bool extra_found = false;
int num_regs = gdbarch_num_regs (gdbarch);

@@ -360,7 +375,7 @@ aarch64_linux_sigframe_init (const struct tramp_frame *self,
/* Check if the section is followed by a full SVE dump, and set
sve_regs if it is. */
gdb_byte buf[4];
- uint16_t vq;
+ uint16_t flags;

if (!tdep->has_sve ())
break;
@@ -373,9 +388,23 @@ aarch64_linux_sigframe_init (const struct tramp_frame *self,
}
vq = sve_vq_from_vl (extract_unsigned_integer (buf, 2, byte_order));

- if (vq != tdep->vq)
- error (_("Invalid vector length in signal frame %d vs %s."), vq,
- pulongest (tdep->vq));
+ /* If SME is supported, also read the flags field. It may
+ indicate if this SVE context is for streaming mode (SSVE). */
+ if (tdep->has_sme ())
+ {
+ if (target_read_memory (section
+ + AARCH64_SVE_CONTEXT_FLAGS_OFFSET,
+ buf, 2) != 0)
+ {
+ section += size;
+ break;
+ }
+ flags = extract_unsigned_integer (buf, 2, byte_order);
+
+ /* Is this SSVE data? If so, enable the SM bit in SVCR. */
+ if (flags & SVE_SIG_FLAG_SM)
+ svcr |= SVCR_SM_BIT;
+ }

if (size >= AARCH64_SVE_CONTEXT_SIZE (vq))
sve_regs = section + AARCH64_SVE_CONTEXT_REGS_OFFSET;
@@ -384,6 +413,38 @@ aarch64_linux_sigframe_init (const struct tramp_frame *self,
break;
}

+ case AARCH64_ZA_MAGIC:
+ {
+ if (!tdep->has_sme ())
+ {
+ section += size;
+ break;
+ }
+
+ /* Check if the section is followed by a full ZA dump, and set
+ za_state if it is. */
+ gdb_byte buf[2];
+
+ if (target_read_memory (section + AARCH64_SME_CONTEXT_SVL_OFFSET,
+ buf, 2) != 0)
+ {
+ section += size;
+ break;
+ }
+ svq = sve_vq_from_vl (extract_unsigned_integer (buf, 2,
+ byte_order));
+
+ if (size >= AARCH64_SME_CONTEXT_SIZE (svq))
+ {
+ za_state = section + AARCH64_SME_CONTEXT_REGS_OFFSET;
+ /* We have ZA data. Enable the ZA bit in SVCR. */
+ svcr |= SVCR_ZA_BIT;
+ }
+
+ section += size;
+ break;
+ }
+
case AARCH64_EXTRA_MAGIC:
{
/* Extra is always the last valid section in reserved and points to
@@ -422,7 +483,7 @@ aarch64_linux_sigframe_init (const struct tramp_frame *self,

for (int i = 0; i < 32; i++)
{
- offset = sve_regs + (i * tdep->vq * 16);
+ offset = sve_regs + (i * vq * 16);
trad_frame_set_reg_addr (this_cache, AARCH64_SVE_Z0_REGNUM + i,
offset);
trad_frame_set_reg_addr (this_cache,
@@ -440,12 +501,12 @@ aarch64_linux_sigframe_init (const struct tramp_frame *self,
offset);
}

- offset = sve_regs + AARCH64_SVE_CONTEXT_P_REGS_OFFSET (tdep->vq);
+ offset = sve_regs + AARCH64_SVE_CONTEXT_P_REGS_OFFSET (vq);
for (int i = 0; i < 16; i++)
trad_frame_set_reg_addr (this_cache, AARCH64_SVE_P0_REGNUM + i,
- offset + (i * tdep->vq * 2));
+ offset + (i * vq * 2));

- offset = sve_regs + AARCH64_SVE_CONTEXT_FFR_OFFSET (tdep->vq);
+ offset = sve_regs + AARCH64_SVE_CONTEXT_FFR_OFFSET (vq);
trad_frame_set_reg_addr (this_cache, AARCH64_SVE_FFR_REGNUM, offset);
}

@@ -461,6 +522,17 @@ aarch64_linux_sigframe_init (const struct tramp_frame *self,
aarch64_linux_restore_vregs (gdbarch, this_cache, fpsimd);
}

+ if (za_state != 0)
+ {
+ /* Restore the ZA state. */
+ trad_frame_set_reg_addr (this_cache, tdep->sme_za_regnum,
+ za_state);
+ }
+
+ /* If SME is supported, set SVCR as well. */
+ if (tdep->has_sme ())
+ trad_frame_set_reg_value (this_cache, tdep->sme_svcr_regnum, svcr);
+
trad_frame_set_id (this_cache, frame_id_build (sp, func));
}

diff --git a/gdb/nat/aarch64-scalable-linux-sigcontext.h b/gdb/nat/aarch64-scalable-linux-sigcontext.h
index 74407bd266a..18623443744 100644
--- a/gdb/nat/aarch64-scalable-linux-sigcontext.h
+++ b/gdb/nat/aarch64-scalable-linux-sigcontext.h
@@ -30,7 +30,10 @@
struct sve_context {
struct _aarch64_ctx head;
__u16 vl;
- __u16 __reserved[3];
+ /* Holds flags. This field was defined for SME support. Prior to it,
+ this used to be a reserved 16-bit value. */
+ __u16 flags;
+ __u16 __reserved[2];
};

/*
--
2.25.1