git: 382ffc87860c - stable/13 - x86: Add a NT_X86_SEGBASES register set.

From: John Baldwin <jhb_at_FreeBSD.org>
Date: Fri, 13 May 2022 17:42:52 UTC
The branch stable/13 has been updated by jhb:

URL: https://cgit.FreeBSD.org/src/commit/?id=382ffc87860cd09f9350179e59bdf88f07b55631

commit 382ffc87860cd09f9350179e59bdf88f07b55631
Author:     John Baldwin <jhb@FreeBSD.org>
AuthorDate: 2022-03-24 18:36:19 +0000
Commit:     John Baldwin <jhb@FreeBSD.org>
CommitDate: 2022-05-13 16:45:19 +0000

    x86: Add a NT_X86_SEGBASES register set.
    
    This register set contains the values of the fsbase and gsbase
    registers.  Note that these registers can already be controlled
    individually via ptrace(2) via MD operations, so the main reason for
    adding this is to include these register values in core dumps.  In
    particular, this will enable looking up the value of TLS variables
    from core dumps in gdb.
    
    The value of NT_X86_SEGBASES was chosen to match the value of
    NT_386_TLS on Linux.  The notes serve similar purposes, but FreeBSD
    will never dump a note equivalent to NT_386_TLS (which dumps a single
    segment descriptor rather than a pair of addresses) and picking a
    currently-unused value in the NT_X86_* range could result in a future
    conflict.
    
    Reviewed by:    markj
    Differential Revision:  https://reviews.freebsd.org/D34650
    
    (cherry picked from commit 931983ee0864079c5f1be0a6b3b9ef097d84ffba)
---
 contrib/elftoolchain/readelf/readelf.c |   1 +
 sys/amd64/amd64/ptrace_machdep.c       | 102 +++++++++++++++++++++++++++++++++
 sys/amd64/ia32/ia32_reg.c              |  50 ++++++++++++++++
 sys/i386/i386/ptrace_machdep.c         |  51 ++++++++++++++++-
 sys/sys/elf_common.h                   |   1 +
 sys/x86/include/reg.h                  |  18 ++++++
 usr.bin/gcore/elfcore.c                |   1 +
 7 files changed, 223 insertions(+), 1 deletion(-)

diff --git a/contrib/elftoolchain/readelf/readelf.c b/contrib/elftoolchain/readelf/readelf.c
index fa3cdca3d682..25dda95f2a50 100644
--- a/contrib/elftoolchain/readelf/readelf.c
+++ b/contrib/elftoolchain/readelf/readelf.c
@@ -1195,6 +1195,7 @@ note_type_freebsd_core(unsigned int nt)
 	case 17: return "NT_PTLWPINFO";
 	case 0x100: return "NT_PPC_VMX (ppc Altivec registers)";
 	case 0x102: return "NT_PPC_VSX (ppc VSX registers)";
+	case 0x200: return "NT_X86_SEGBASES (x86 segment base registers)";
 	case 0x202: return "NT_X86_XSTATE (x86 XSAVE extended state)";
 	case 0x400: return "NT_ARM_VFP (arm VFP registers)";
 	case 0x401: return "NT_ARM_TLS (arm TLS register)";
diff --git a/sys/amd64/amd64/ptrace_machdep.c b/sys/amd64/amd64/ptrace_machdep.c
index 74fd48c68492..069a5b4cdb9d 100644
--- a/sys/amd64/amd64/ptrace_machdep.c
+++ b/sys/amd64/amd64/ptrace_machdep.c
@@ -32,11 +32,13 @@ __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
 #include <sys/systm.h>
+#include <sys/elf.h>
 #include <sys/lock.h>
 #include <sys/malloc.h>
 #include <sys/mutex.h>
 #include <sys/proc.h>
 #include <sys/ptrace.h>
+#include <sys/reg.h>
 #include <sys/sysent.h>
 #include <vm/vm.h>
 #include <vm/pmap.h>
@@ -52,6 +54,106 @@ struct ptrace_xstate_info32 {
 };
 #endif
 
+static bool
+get_segbases(struct regset *rs, struct thread *td, void *buf,
+    size_t *sizep)
+{
+	struct segbasereg *reg;
+	struct pcb *pcb;
+
+	if (buf != NULL) {
+		KASSERT(*sizep == sizeof(*reg), ("%s: invalid size", __func__));
+		reg = buf;
+
+		pcb = td->td_pcb;
+		if (td == curthread)
+			update_pcb_bases(pcb);
+		reg->r_fsbase = pcb->pcb_fsbase;
+		reg->r_gsbase = pcb->pcb_gsbase;
+	}
+	*sizep = sizeof(*reg);
+	return (true);
+}
+
+static bool
+set_segbases(struct regset *rs, struct thread *td, void *buf,
+    size_t size)
+{
+	struct segbasereg *reg;
+	struct pcb *pcb;
+
+	KASSERT(size == sizeof(*reg), ("%s: invalid size", __func__));
+	reg = buf;
+
+	pcb = td->td_pcb;
+	set_pcb_flags(pcb, PCB_FULL_IRET);
+	pcb->pcb_fsbase = reg->r_fsbase;
+	td->td_frame->tf_fs = _ufssel;
+	pcb->pcb_gsbase = reg->r_gsbase;
+	td->td_frame->tf_gs = _ugssel;
+
+	return (true);
+}
+
+static struct regset regset_segbases = {
+	.note = NT_X86_SEGBASES,
+	.size = sizeof(struct segbasereg),
+	.get = get_segbases,
+	.set = set_segbases,
+};
+ELF_REGSET(regset_segbases);
+
+#ifdef COMPAT_FREEBSD32
+static bool
+get_segbases32(struct regset *rs, struct thread *td, void *buf,
+    size_t *sizep)
+{
+	struct segbasereg32 *reg;
+	struct pcb *pcb;
+
+	if (buf != NULL) {
+		KASSERT(*sizep == sizeof(*reg), ("%s: invalid size", __func__));
+		reg = buf;
+
+		pcb = td->td_pcb;
+		if (td == curthread)
+			update_pcb_bases(pcb);
+		reg->r_fsbase = (uint32_t)pcb->pcb_fsbase;
+		reg->r_gsbase = (uint32_t)pcb->pcb_gsbase;
+	}
+	*sizep = sizeof(*reg);
+	return (true);
+}
+
+static bool
+set_segbases32(struct regset *rs, struct thread *td, void *buf,
+    size_t size)
+{
+	struct segbasereg32 *reg;
+	struct pcb *pcb;
+
+	KASSERT(size == sizeof(*reg), ("%s: invalid size", __func__));
+	reg = buf;
+
+	pcb = td->td_pcb;
+	set_pcb_flags(pcb, PCB_FULL_IRET);
+	pcb->pcb_fsbase = reg->r_fsbase;
+	td->td_frame->tf_fs = _ufssel;
+	pcb->pcb_gsbase = reg->r_gsbase;
+	td->td_frame->tf_gs = _ugssel;
+
+	return (true);
+}
+
+static struct regset regset_segbases32 = {
+	.note = NT_X86_SEGBASES,
+	.size = sizeof(struct segbasereg32),
+	.get = get_segbases32,
+	.set = set_segbases32,
+};
+ELF32_REGSET(regset_segbases32);
+#endif
+
 static int
 cpu_ptrace_xstate(struct thread *td, int req, void *addr, int data)
 {
diff --git a/sys/amd64/ia32/ia32_reg.c b/sys/amd64/ia32/ia32_reg.c
index 343d1564e1ff..539a268ef350 100644
--- a/sys/amd64/ia32/ia32_reg.c
+++ b/sys/amd64/ia32/ia32_reg.c
@@ -32,6 +32,7 @@
 __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
+#include <sys/elf.h>
 #include <sys/exec.h>
 #include <sys/fcntl.h>
 #include <sys/imgact.h>
@@ -266,3 +267,52 @@ set_dbregs32(struct thread *td, struct dbreg32 *regs)
 		dr.dr[i] = 0;
 	return (set_dbregs(td, &dr));
 }
+
+static bool
+get_i386_segbases(struct regset *rs, struct thread *td, void *buf,
+    size_t *sizep)
+{
+	struct segbasereg32 *reg;
+	struct pcb *pcb;
+
+	if (buf != NULL) {
+		KASSERT(*sizep == sizeof(*reg), ("%s: invalid size", __func__));
+		reg = buf;
+
+		pcb = td->td_pcb;
+		if (td == curthread)
+			update_pcb_bases(pcb);
+		reg->r_fsbase = pcb->pcb_fsbase;
+		reg->r_gsbase = pcb->pcb_gsbase;
+	}
+	*sizep = sizeof(*reg);
+	return (true);
+}
+
+static bool
+set_i386_segbases(struct regset *rs, struct thread *td, void *buf,
+    size_t size)
+{
+	struct segbasereg32 *reg;
+	struct pcb *pcb;
+
+	KASSERT(size == sizeof(*reg), ("%s: invalid size", __func__));
+	reg = buf;
+
+	pcb = td->td_pcb;
+	set_pcb_flags(pcb, PCB_FULL_IRET);
+	pcb->pcb_fsbase = reg->r_fsbase;
+	td->td_frame->tf_fs = _ufssel;
+	pcb->pcb_gsbase = reg->r_gsbase;
+	td->td_frame->tf_gs = _ugssel;
+
+	return (true);
+}
+
+static struct regset regset_i386_segbases = {
+	.note = NT_X86_SEGBASES,
+	.size = sizeof(struct segbasereg),
+	.get = get_i386_segbases,
+	.set = set_i386_segbases,
+};
+ELF32_REGSET(regset_i386_segbases);
diff --git a/sys/i386/i386/ptrace_machdep.c b/sys/i386/i386/ptrace_machdep.c
index 7ddc697502cf..29551336f8a6 100644
--- a/sys/i386/i386/ptrace_machdep.c
+++ b/sys/i386/i386/ptrace_machdep.c
@@ -34,15 +34,64 @@ __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
 #include <sys/systm.h>
+#include <sys/elf.h>
 #include <sys/lock.h>
 #include <sys/malloc.h>
 #include <sys/mutex.h>
 #include <sys/proc.h>
 #include <sys/ptrace.h>
+#include <sys/reg.h>
 #include <machine/frame.h>
 #include <machine/md_var.h>
 #include <machine/pcb.h>
 
+static uint32_t
+get_segbase(struct segment_descriptor *sdp)
+{
+	return (sdp->sd_hibase << 24 | sdp->sd_lobase);
+}
+
+static bool
+get_segbases(struct regset *rs, struct thread *td, void *buf,
+    size_t *sizep)
+{
+	struct segbasereg *reg;
+
+	if (buf != NULL) {
+		KASSERT(*sizep == sizeof(*reg), ("%s: invalid size", __func__));
+		reg = buf;
+		reg->r_fsbase = get_segbase(&td->td_pcb->pcb_fsd);
+		reg->r_gsbase = get_segbase(&td->td_pcb->pcb_gsd);
+	}
+	*sizep = sizeof(*reg);
+	return (true);
+}
+
+static bool
+set_segbases(struct regset *rs, struct thread *td, void *buf,
+    size_t size)
+{
+	struct segbasereg *reg;
+
+	KASSERT(size == sizeof(*reg), ("%s: invalid size", __func__));
+	reg = buf;
+
+	fill_based_sd(&td->td_pcb->pcb_fsd, reg->r_fsbase);
+	td->td_frame->tf_fs = GSEL(GUFS_SEL, SEL_UPL);
+	fill_based_sd(&td->td_pcb->pcb_gsd, reg->r_gsbase);
+	td->td_pcb->pcb_gs = GSEL(GUGS_SEL, SEL_UPL);
+
+	return (true);
+}
+
+static struct regset regset_segbases = {
+	.note = NT_X86_SEGBASES,
+	.size = sizeof(struct segbasereg),
+	.get = get_segbases,
+	.set = set_segbases,
+};
+ELF_REGSET(regset_segbases);
+
 static int
 cpu_ptrace_xstate(struct thread *td, int req, void *addr, int data)
 {
@@ -173,7 +222,7 @@ cpu_ptrace(struct thread *td, int req, void *addr, int data)
 	case PT_GETGSBASE:
 		sdp = req == PT_GETFSBASE ? &td->td_pcb->pcb_fsd :
 		    &td->td_pcb->pcb_gsd;
-		r = sdp->sd_hibase << 24 | sdp->sd_lobase;
+		r = get_segbase(sdp);
 		error = copyout(&r, addr, sizeof(r));
 		break;
 
diff --git a/sys/sys/elf_common.h b/sys/sys/elf_common.h
index 3c88b59cb5ce..d4508f0750a8 100644
--- a/sys/sys/elf_common.h
+++ b/sys/sys/elf_common.h
@@ -823,6 +823,7 @@ typedef struct {
 #define	NT_PTLWPINFO		17	/* Thread ptrace miscellaneous info. */
 #define	NT_PPC_VMX	0x100	/* PowerPC Altivec/VMX registers */
 #define	NT_PPC_VSX	0x102	/* PowerPC VSX registers */
+#define	NT_X86_SEGBASES	0x200	/* x86 FS/GS base addresses. */
 #define	NT_X86_XSTATE	0x202	/* x86 XSAVE extended state. */
 #define	NT_ARM_VFP	0x400	/* ARM VFP registers */
 #define	NT_ARM_TLS	0x401	/* ARM TLS register */
diff --git a/sys/x86/include/reg.h b/sys/x86/include/reg.h
index f97704d63245..3e39ffe3e263 100644
--- a/sys/x86/include/reg.h
+++ b/sys/x86/include/reg.h
@@ -86,6 +86,7 @@
 #define	__reg32		reg
 #define	__fpreg32	fpreg
 #define	__dbreg32	dbreg
+#define	__segbasereg32	segbasereg
 #else
 #define	__reg32		reg32
 #define	__reg64		reg
@@ -93,6 +94,8 @@
 #define	__fpreg64	fpreg
 #define	__dbreg32	dbreg32
 #define	__dbreg64	dbreg
+#define	__segbasereg32	segbasereg32
+#define	__segbasereg64	segbasereg
 #define	__HAVE_REG32
 #endif
 
@@ -236,12 +239,27 @@ struct __dbreg64 {
 #define	DBREG_DRX(d,x)	((d)->dr[(x)])	/* reference dr0 - dr7 by
 					   register number */
 
+/*
+ * Register set accessible via NT_X86_SEGBASES.
+ */
+struct __segbasereg32 {
+	__uint32_t	r_fsbase;
+	__uint32_t	r_gsbase;
+};
+
+struct __segbasereg64 {
+	__uint64_t	r_fsbase;
+	__uint64_t	r_gsbase;
+};
+
 #undef __reg32
 #undef __reg64
 #undef __fpreg32
 #undef __fpreg64
 #undef __dbreg32
 #undef __dbreg64
+#undef __segbasereg32
+#undef __segbasereg64
 
 #ifdef _KERNEL
 /*
diff --git a/usr.bin/gcore/elfcore.c b/usr.bin/gcore/elfcore.c
index c3ef36938ea9..1fcd14698a9e 100644
--- a/usr.bin/gcore/elfcore.c
+++ b/usr.bin/gcore/elfcore.c
@@ -379,6 +379,7 @@ elf_putnotes(pid_t pid, struct sbuf *sb, size_t *sizep)
 		elf_putregnote(NT_ARM_VFP, tids[i], sb);
 #endif
 #if defined(__i386__) || defined(__amd64__)
+		elf_putregnote(NT_X86_SEGBASES, tids[i], sb);
 		elf_putnote(NT_X86_XSTATE, elf_note_x86_xstate, tids + i, sb);
 #endif
 #if defined(__powerpc__)