[PATCH 1/8] gdb/riscv: use a single regset supply function for riscv fbsd & linux

Andrew Burgess
2020-12-02T17:39:43Z

The RISC-V x0 register is hard-coded to zero. As such neither Linux
or FreeBSD supply the value of the register x0 in their core dump
files.

For FreeBSD we take care of this by manually supplying the value of x0
in riscv_fbsd_supply_gregset, however we don't do this for Linux. As
a result after loading a core file on Linux we see this behaviour:

(gdb) p $x0
$1 = <unavailable>

In this commit I make riscv_fbsd_supply_gregset a common function that
can be shared between RISC-V for FreeBSD and Linux, this resolves the
above issue.

There is a similar problem for the two registers `fflags` and `frm`.
These two floating point related CSRs are a little weird. They are
separate CSRs in the RISC-V specification, but are actually sub-fields
of the `fcsr` CSR.

As a result neither Linux or FreeBSD supply the `fflags` or `frm`
registers as separate fields in their core dumps, and so, after
restoring a core dump these register are similarly unavailable.

In this commit I supply `fflags` and `frm` by first asking for the
value of `fcsr`, extracting the two fields, and using these to supply
the values for `fflags` and `frm`.

gdb/ChangeLog:

* riscv-fbsd-tdep.c (riscv_fbsd_supply_gregset): Delete.
(riscv_fbsd_gregset): Use riscv_supply_regset.
(riscv_fbsd_fpregset): Likewise.
* riscv-linux-tdep.c (riscv_linux_gregset): Likewise.
(riscv_linux_fregset): Likewise.
* riscv-tdep.c (riscv_supply_regset): Define new function.
* riscv-tdep.h (riscv_supply_regset): Declare new function.
---
gdb/ChangeLog | 10 +++++++++
gdb/riscv-fbsd-tdep.c | 20 ++---------------
gdb/riscv-linux-tdep.c | 4 ++--
gdb/riscv-tdep.c | 50 ++++++++++++++++++++++++++++++++++++++++++
gdb/riscv-tdep.h | 23 +++++++++++++++++++
5 files changed, 87 insertions(+), 20 deletions(-)

diff --git a/gdb/riscv-fbsd-tdep.c b/gdb/riscv-fbsd-tdep.c
index 6e0eb2bb788..f9eaaa16b25 100644
--- a/gdb/riscv-fbsd-tdep.c
+++ b/gdb/riscv-fbsd-tdep.c
@@ -53,32 +53,16 @@ static const struct regcache_map_entry riscv_fbsd_fpregmap[] =
{ 0 }
};

-/* Supply the general-purpose registers stored in GREGS to REGCACHE.
- This function only exists to supply the always-zero x0 in addition
- to the registers in GREGS. */
-
-static void
-riscv_fbsd_supply_gregset (const struct regset *regset,
- struct regcache *regcache, int regnum,
- const void *gregs, size_t len)
-{
- regcache->supply_regset (&riscv_fbsd_gregset, regnum, gregs, len);
- if (regnum == -1 || regnum == RISCV_ZERO_REGNUM)
- regcache->raw_supply_zeroed (RISCV_ZERO_REGNUM);
-}
-
/* Register set definitions. */

const struct regset riscv_fbsd_gregset =
{
- riscv_fbsd_gregmap,
- riscv_fbsd_supply_gregset, regcache_collect_regset
+ riscv_fbsd_gregmap, riscv_supply_regset, regcache_collect_regset
};

const struct regset riscv_fbsd_fpregset =
{
- riscv_fbsd_fpregmap,
- regcache_supply_regset, regcache_collect_regset
+ riscv_fbsd_fpregmap, riscv_supply_regset, regcache_collect_regset
};

/* Implement the "iterate_over_regset_sections" gdbarch method. */
diff --git a/gdb/riscv-linux-tdep.c b/gdb/riscv-linux-tdep.c
index fce838097e2..86dd536edf4 100644
--- a/gdb/riscv-linux-tdep.c
+++ b/gdb/riscv-linux-tdep.c
@@ -52,14 +52,14 @@ static const struct regcache_map_entry riscv_linux_fregmap[] =

static const struct regset riscv_linux_gregset =
{
- riscv_linux_gregmap, regcache_supply_regset, regcache_collect_regset
+ riscv_linux_gregmap, riscv_supply_regset, regcache_collect_regset
};

/* Define the FP register regset. */

static const struct regset riscv_linux_fregset =
{
- riscv_linux_fregmap, regcache_supply_regset, regcache_collect_regset
+ riscv_linux_fregmap, riscv_supply_regset, regcache_collect_regset
};

/* Define hook for core file support. */
diff --git a/gdb/riscv-tdep.c b/gdb/riscv-tdep.c
index 4e255056863..a428f79940d 100644
--- a/gdb/riscv-tdep.c
+++ b/gdb/riscv-tdep.c
@@ -3693,6 +3693,56 @@ riscv_init_reggroups ()
csr_reggroup = reggroup_new ("csr", USER_REGGROUP);
}

+/* See riscv-tdep.h. */
+
+void
+riscv_supply_regset (const struct regset *regset,
+ struct regcache *regcache, int regnum,
+ const void *regs, size_t len)
+{
+ regcache->supply_regset (regset, regnum, regs, len);
+
+ if (regnum == -1 || regnum == RISCV_ZERO_REGNUM)
+ regcache->raw_supply_zeroed (RISCV_ZERO_REGNUM);
+
+ if (regnum == -1 || regnum == RISCV_CSR_FFLAGS_REGNUM
+ || regnum == RISCV_CSR_FRM_REGNUM)
+ {
+ int fcsr_regnum = RISCV_CSR_FCSR_REGNUM;
+
+ /* Ensure that FCSR has been read into REGCACHE. */
+ if (regnum != -1)
+ regcache->supply_regset (regset, fcsr_regnum, regs, len);
+
+ /* Grab the FCSR value if it is now in the regcache. We must check
+ the status first as, if the register was not supplied by REGSET,
+ this call will trigger a recursive attempt to fetch the
+ registers. */
+ if (regcache->get_register_status (fcsr_regnum) == REG_VALID)
+ {
+ ULONGEST fcsr_val;
+ regcache->raw_read (fcsr_regnum, &fcsr_val);
+
+ /* Extract the fflags and frm values. */
+ ULONGEST fflags_val = fcsr_val & 0x1f;
+ ULONGEST frm_val = (fcsr_val >> 5) & 0x7;
+
+ /* And supply these if needed. */
+ if (regnum == -1 || regnum == RISCV_CSR_FFLAGS_REGNUM)
+ regcache->raw_supply_integer (RISCV_CSR_FFLAGS_REGNUM,
+ (gdb_byte *) &fflags_val,
+ sizeof (fflags_val),
+ /* is_signed */ false);
+
+ if (regnum == -1 || regnum == RISCV_CSR_FRM_REGNUM)
+ regcache->raw_supply_integer (RISCV_CSR_FRM_REGNUM,
+ (gdb_byte *)&frm_val,
+ sizeof (fflags_val),
+ /* is_signed */ false);
+ }
+ }
+}
+
void _initialize_riscv_tdep ();
void
_initialize_riscv_tdep ()
diff --git a/gdb/riscv-tdep.h b/gdb/riscv-tdep.h
index 5bd3314d450..1064ced1192 100644
--- a/gdb/riscv-tdep.h
+++ b/gdb/riscv-tdep.h
@@ -132,4 +132,27 @@ extern int riscv_abi_flen (struct gdbarch *gdbarch);
extern std::vector<CORE_ADDR> riscv_software_single_step
(struct regcache *regcache);

+/* Supply register REGNUM from the buffer REGS (length LEN) into
+ REGCACHE. REGSET describes the layout of the buffer. If REGNUM is -1
+ then all registers described by REGSET are supplied.
+
+ The register RISCV_ZERO_REGNUM should not be described by REGSET,
+ however, this register (which always has the value 0) will be supplied
+ by this function if requested.
+
+ The registers RISCV_CSR_FFLAGS_REGNUM and RISCV_CSR_FRM_REGNUM should
+ not be described by REGSET, however, these register will be provided if
+ requested assuming either:
+ (a) REGCACHE already contains the value of RISCV_CSR_FCSR_REGNUM, or
+ (b) REGSET describes the location of RISCV_CSR_FCSR_REGNUM in the REGS
+ buffer.
+
+ This function can be used as the supply function for either x-regs or
+ f-regs when loading corefiles, and doesn't care which abi is currently
+ in use. */
+
+extern void riscv_supply_regset (const struct regset *regset,
+ struct regcache *regcache, int regnum,
+ const void *regs, size_t len);
+
#endif /* RISCV_TDEP_H */
--
2.25.4