[1/4] RISC-V/Linux/native: Determine FLEN dynamically
Commit Message
Fix RISC-V native Linux support to handle a 64-bit FPU (FLEN == 64) with
both RV32 and RV64 systems, which is a part of the current Linux ABI for
hard-float systems, rather than assuming that (FLEN == XLEN).
We can do better however and not rely on any particular value of FLEN
and probe for it dynamically, by observing that the PTRACE_GETREGSET
ptrace(2) call will only accept an exact regset size, and that will
reflect FLEN. Therefore iterate over the call with a geometrically
increasing regset size until a match is marked by a successful ptrace(2)
call completion or we run beyond the maximum size we can support.
Also handle a glibc bug where ELF_NFPREG is defined in terms of NFPREG,
however NFPREG is nowhere defined.
gdb/
* riscv-linux-nat.c [!NFPREG] (NFPREG): New macro.
(riscv_linux_nat_target::read_description): Determine FLEN
dynamically.
---
Hi,
Smoke-testing indicates no immediate problems with this change; full
regression-testing is still running and will take approximately 3 days.
Maciej
---
gdb/riscv-linux-nat.c | 49 +++++++++++++++++++++++++++++++++++++------------
1 file changed, 37 insertions(+), 12 deletions(-)
gdb-riscv-linux-nat-flen.diff
Comments
On Thu, Jan 23, 2020 at 11:40 AM Maciej W. Rozycki <macro@wdc.com> wrote:
> gdb/
> * riscv-linux-nat.c [!NFPREG] (NFPREG): New macro.
> (riscv_linux_nat_target::read_description): Determine FLEN
> dynamically.
This looks good to me, though I'm not a formal riscv linux gdb maintainer.
Jim
===================================================================
@@ -28,6 +28,11 @@
#include <sys/ptrace.h>
+/* Work around glibc header breakage causing ELF_NFPREG not to be usable. */
+#ifndef NFPREG
+# define NFPREG 33
+#endif
+
/* RISC-V Linux native additions to the default linux support. */
class riscv_linux_nat_target final : public linux_nat_target
@@ -166,8 +171,8 @@ const struct target_desc *
riscv_linux_nat_target::read_description ()
{
struct riscv_gdbarch_features features;
- struct iovec iov;
elf_fpregset_t regs;
+ int flen;
int tid;
/* Figuring out xlen is easy. */
@@ -175,19 +180,39 @@ riscv_linux_nat_target::read_description
tid = inferior_ptid.lwp ();
- iov.iov_base = ®s;
- iov.iov_len = sizeof (regs);
+ /* Start with no f-registers. */
+ features.flen = 0;
- /* Can we fetch the f-registers? */
- if (ptrace (PTRACE_GETREGSET, tid, NT_FPREGSET,
- (PTRACE_TYPE_ARG3) &iov) == -1)
- features.flen = 0; /* No f-registers. */
- else
+ /* How much worth of f-registers can we fetch if any? */
+ for (flen = sizeof (regs.__f.__f[0]); ; flen *= 2)
{
- /* TODO: We need a way to figure out the actual length of the
- f-registers. We could have 64-bit x-registers, with 32-bit
- f-registers. For now, just assumed xlen and flen match. */
- features.flen = features.xlen;
+ size_t regset_size;
+ struct iovec iov;
+
+ /* Regsets have a uniform slot size, so we count FSCR like an FGR. */
+ regset_size = ELF_NFPREG * flen;
+ if (regset_size > sizeof (regs))
+ break;
+
+ iov.iov_base = ®s;
+ iov.iov_len = regset_size;
+ if (ptrace (PTRACE_GETREGSET, tid, NT_FPREGSET,
+ (PTRACE_TYPE_ARG3) &iov) == -1)
+ {
+ switch (errno)
+ {
+ case EINVAL:
+ continue;
+ case EIO:
+ break;
+ default:
+ perror_with_name (_("Couldn't get registers"));
+ break;
+ }
+ }
+ else
+ features.flen = flen;
+ break;
}
return riscv_create_target_description (features);