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To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org,
dev-commits-src-main@FreeBSD.org
From: Mitchell Horne <mhorne@FreeBSD.org>
Subject: git: 701923e2a410 - main - riscv: improve parsing of riscv,isa property strings
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The branch main has been updated by mhorne:
URL: https://cgit.FreeBSD.org/src/commit/?id=701923e2a4105be606c5263181b6eb6f546f1a84
commit 701923e2a4105be606c5263181b6eb6f546f1a84
Author: Mitchell Horne <mhorne@FreeBSD.org>
AuthorDate: 2022-10-28 16:28:08 +0000
Commit: Mitchell Horne <mhorne@FreeBSD.org>
CommitDate: 2022-10-28 16:28:08 +0000
riscv: improve parsing of riscv,isa property strings
This code was originally written under the assumption that the ISA
string would only contain single-letter extensions. The RISC-V
specification has extended its description of the format quite a bit,
allowing for much longer ISA strings containing multi-letter extension
names.
Newer versions of QEMU (7.1.0) will append to the riscv,isa property
indicating the presence of multi-letter standard extensions such as
Zfencei. This triggers a KASSERT about the expected length of the
string, preventing boot.
Increase the size of the isa array significantly, and teach the code
to parse (skip over) multi-letter extensions, and optional extension
version numbers. We currently ignore them completely, but this will
change in the future as we start supporting supervisor-level extensions.
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D36601
---
sys/riscv/include/elf.h | 14 ++--
sys/riscv/riscv/identcpu.c | 182 ++++++++++++++++++++++++++++++++++++++++-----
2 files changed, 169 insertions(+), 27 deletions(-)
diff --git a/sys/riscv/include/elf.h b/sys/riscv/include/elf.h
index 671e2d2617c0..c0817d8fb47b 100644
--- a/sys/riscv/include/elf.h
+++ b/sys/riscv/include/elf.h
@@ -75,13 +75,13 @@ __ElfType(Auxinfo);
#define ET_DYN_LOAD_ADDR 0x100000
/* Flags passed in AT_HWCAP */
-#define HWCAP_ISA_BIT(c) (1 << ((c) - 'A'))
-#define HWCAP_ISA_I HWCAP_ISA_BIT('I')
-#define HWCAP_ISA_M HWCAP_ISA_BIT('M')
-#define HWCAP_ISA_A HWCAP_ISA_BIT('A')
-#define HWCAP_ISA_F HWCAP_ISA_BIT('F')
-#define HWCAP_ISA_D HWCAP_ISA_BIT('D')
-#define HWCAP_ISA_C HWCAP_ISA_BIT('C')
+#define HWCAP_ISA_BIT(c) (1 << ((c) - 'a'))
+#define HWCAP_ISA_I HWCAP_ISA_BIT('i')
+#define HWCAP_ISA_M HWCAP_ISA_BIT('m')
+#define HWCAP_ISA_A HWCAP_ISA_BIT('a')
+#define HWCAP_ISA_F HWCAP_ISA_BIT('f')
+#define HWCAP_ISA_D HWCAP_ISA_BIT('d')
+#define HWCAP_ISA_C HWCAP_ISA_BIT('c')
#define HWCAP_ISA_G \
(HWCAP_ISA_I | HWCAP_ISA_M | HWCAP_ISA_A | HWCAP_ISA_F | HWCAP_ISA_D)
diff --git a/sys/riscv/riscv/identcpu.c b/sys/riscv/riscv/identcpu.c
index f3afa9b8c7ea..4c151eb47939 100644
--- a/sys/riscv/riscv/identcpu.c
+++ b/sys/riscv/riscv/identcpu.c
@@ -39,6 +39,7 @@ __FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/systm.h>
+#include <sys/ctype.h>
#include <sys/kernel.h>
#include <sys/pcpu.h>
#include <sys/sysctl.h>
@@ -104,34 +105,171 @@ const struct cpu_implementers cpu_implementers[] = {
CPU_IMPLEMENTER_NONE,
};
-#ifdef FDT
/*
- * The ISA string is made up of a small prefix (e.g. rv64) and up to 26 letters
- * indicating the presence of the 26 possible standard extensions. Therefore 32
- * characters will be sufficient.
+ * The ISA string describes the complete set of instructions supported by a
+ * RISC-V CPU. The string begins with a small prefix (e.g. rv64) indicating the
+ * base ISA. It is followed first by single-letter ISA extensions, and then
+ * multi-letter ISA extensions.
+ *
+ * Underscores are used mainly to separate consecutive multi-letter extensions,
+ * but may optionally appear between any two extensions. An extension may be
+ * followed by a version number, in the form of 'Mpm', where M is the
+ * extension's major version number, and 'm' is the minor version number.
+ *
+ * The format is described in detail by the "ISA Extension Naming Conventions"
+ * chapter of the unprivileged spec.
*/
-#define ISA_NAME_MAXLEN 32
#define ISA_PREFIX ("rv" __XSTRING(__riscv_xlen))
#define ISA_PREFIX_LEN (sizeof(ISA_PREFIX) - 1)
+static __inline int
+parse_ext_s(char *isa, int idx, int len)
+{
+ /*
+ * Proceed to the next multi-letter extension or the end of the
+ * string.
+ *
+ * TODO: parse these once we gain support
+ */
+ while (isa[idx] != '_' && idx < len) {
+ idx++;
+ }
+
+ return (idx);
+}
+
+static __inline int
+parse_ext_x(char *isa, int idx, int len)
+{
+ /*
+ * Proceed to the next multi-letter extension or the end of the
+ * string.
+ */
+ while (isa[idx] != '_' && idx < len) {
+ idx++;
+ }
+
+ return (idx);
+}
+
+static __inline int
+parse_ext_z(char *isa, int idx, int len)
+{
+ /*
+ * Proceed to the next multi-letter extension or the end of the
+ * string.
+ *
+ * TODO: parse some of these.
+ */
+ while (isa[idx] != '_' && idx < len) {
+ idx++;
+ }
+
+ return (idx);
+}
+
+static __inline int
+parse_ext_version(char *isa, int idx, u_int *majorp __unused,
+ u_int *minorp __unused)
+{
+ /* Major version. */
+ while (isdigit(isa[idx]))
+ idx++;
+
+ if (isa[idx] != 'p')
+ return (idx);
+ else
+ idx++;
+
+ /* Minor version. */
+ while (isdigit(isa[idx]))
+ idx++;
+
+ return (idx);
+}
+
+/*
+ * Parse the ISA string, building up the set of HWCAP bits as they are found.
+ */
static void
-fill_elf_hwcap(void *dummy __unused)
+parse_riscv_isa(char *isa, int len, u_long *hwcapp)
{
- u_long caps[256] = {0};
- char isa[ISA_NAME_MAXLEN];
u_long hwcap;
- phandle_t node;
- ssize_t len;
int i;
- caps['i'] = caps['I'] = HWCAP_ISA_I;
- caps['m'] = caps['M'] = HWCAP_ISA_M;
- caps['a'] = caps['A'] = HWCAP_ISA_A;
+ hwcap = 0;
+ i = ISA_PREFIX_LEN;
+ while (i < len) {
+ switch(isa[i]) {
+ case 'a':
+ case 'c':
#ifdef FPE
- caps['f'] = caps['F'] = HWCAP_ISA_F;
- caps['d'] = caps['D'] = HWCAP_ISA_D;
+ case 'd':
+ case 'f':
#endif
- caps['c'] = caps['C'] = HWCAP_ISA_C;
+ case 'i':
+ case 'm':
+ hwcap |= HWCAP_ISA_BIT(isa[i]);
+ i++;
+ break;
+ case 'g':
+ hwcap |= HWCAP_ISA_G;
+ i++;
+ break;
+ case 's':
+ /*
+ * XXX: older versions of this string erroneously
+ * indicated supervisor and user mode support as
+ * single-letter extensions. Detect and skip both 's'
+ * and 'u'.
+ */
+ if (isa[i - 1] != '_' && isa[i + 1] == 'u') {
+ i += 2;
+ continue;
+ }
+
+ /*
+ * Supervisor-level extension namespace.
+ */
+ i = parse_ext_s(isa, i, len);
+ break;
+ case 'x':
+ /*
+ * Custom extension namespace. For now, we ignore
+ * these.
+ */
+ i = parse_ext_x(isa, i, len);
+ break;
+ case 'z':
+ /*
+ * Multi-letter standard extension namespace.
+ */
+ i = parse_ext_z(isa, i, len);
+ break;
+ case '_':
+ i++;
+ continue;
+ default:
+ /* Unrecognized/unsupported. */
+ i++;
+ break;
+ }
+
+ i = parse_ext_version(isa, i, NULL, NULL);
+ }
+
+ if (hwcapp != NULL)
+ *hwcapp = hwcap;
+}
+
+#ifdef FDT
+static void
+fill_elf_hwcap(void *dummy __unused)
+{
+ char isa[1024];
+ u_long hwcap;
+ phandle_t node;
+ ssize_t len;
node = OF_finddevice("/cpus");
if (node == -1) {
@@ -152,7 +290,7 @@ fill_elf_hwcap(void *dummy __unused)
continue;
len = OF_getprop(node, "riscv,isa", isa, sizeof(isa));
- KASSERT(len <= ISA_NAME_MAXLEN, ("ISA string truncated"));
+ KASSERT(len <= sizeof(isa), ("ISA string truncated"));
if (len == -1) {
if (bootverbose)
printf("fill_elf_hwcap: "
@@ -165,9 +303,13 @@ fill_elf_hwcap(void *dummy __unused)
return;
}
- hwcap = 0;
- for (i = ISA_PREFIX_LEN; i < len; i++)
- hwcap |= caps[(unsigned char)isa[i]];
+ /*
+ * The string is specified to be lowercase, but let's be
+ * certain.
+ */
+ for (int i = 0; i < len; i++)
+ isa[i] = tolower(isa[i]);
+ parse_riscv_isa(isa, len, &hwcap);
if (elf_hwcap != 0)
elf_hwcap &= hwcap;