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riscv: improve parsing of riscv,isa property strings

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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
This commit is contained in:
Mitchell Horne 2022-10-28 13:28:08 -03:00
parent 5723d13811
commit 701923e2a4
2 changed files with 170 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
sys/riscv/include/elf.h
View File

@ -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)

184
sys/riscv/riscv/identcpu.c
View File

@ -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
parse_riscv_isa(char *isa, int len, u_long *hwcapp)
{
u_long hwcap;
int i;
hwcap = 0;
i = ISA_PREFIX_LEN;
while (i < len) {
switch(isa[i]) {
case 'a':
case 'c':
#ifdef FPE
case 'd':
case 'f':
#endif
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)
{
u_long caps[256] = {0};
char isa[ISA_NAME_MAXLEN];
char isa[1024];
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;
#ifdef FPE
caps['f'] = caps['F'] = HWCAP_ISA_F;
caps['d'] = caps['D'] = HWCAP_ISA_D;
#endif
caps['c'] = caps['C'] = HWCAP_ISA_C;
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;