Le 29/04/2021 à 10:06, Arnd Bergmann a écrit :
From: Arnd Bergmann <a...@arndb.de> gcc-11 points out that modifying local variables next to a longjmp/setjmp may cause undefined behavior: arch/powerpc/kexec/crash.c: In function 'crash_kexec_prepare_cpus.constprop': arch/powerpc/kexec/crash.c:108:22: error: variable 'ncpus' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbere d] arch/powerpc/kexec/crash.c:109:13: error: variable 'tries' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbere d] arch/powerpc/xmon/xmon.c: In function 'xmon_print_symbol': arch/powerpc/xmon/xmon.c:3625:21: error: variable 'name' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered] arch/powerpc/xmon/xmon.c: In function 'stop_spus': arch/powerpc/xmon/xmon.c:4057:13: error: variable 'i' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered] arch/powerpc/xmon/xmon.c: In function 'restart_spus': arch/powerpc/xmon/xmon.c:4098:13: error: variable 'i' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered] arch/powerpc/xmon/xmon.c: In function 'dump_opal_msglog': arch/powerpc/xmon/xmon.c:3008:16: error: variable 'pos' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered] arch/powerpc/xmon/xmon.c: In function 'show_pte': arch/powerpc/xmon/xmon.c:3207:29: error: variable 'tsk' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered] arch/powerpc/xmon/xmon.c: In function 'show_tasks': arch/powerpc/xmon/xmon.c:3302:29: error: variable 'tsk' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered] arch/powerpc/xmon/xmon.c: In function 'xmon_core': arch/powerpc/xmon/xmon.c:494:13: error: variable 'cmd' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered] arch/powerpc/xmon/xmon.c:860:21: error: variable 'bp' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered] arch/powerpc/xmon/xmon.c:860:21: error: variable 'bp' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered] arch/powerpc/xmon/xmon.c:492:48: error: argument 'fromipi' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered] According to the documentation, marking these as 'volatile' is sufficient to avoid the problem, and it shuts up the warning.
I think this change deserves some comment in the code, and maybe also an update of https://www.kernel.org/doc/html/latest/process/volatile-considered-harmful.html
Otherwise, there's a risk that one day or another, someone removes those 'volatile' markings. Christophe
Signed-off-by: Arnd Bergmann <a...@arndb.de> --- arch/powerpc/kexec/crash.c | 4 ++-- arch/powerpc/xmon/xmon.c | 22 +++++++++++----------- 2 files changed, 13 insertions(+), 13 deletions(-) diff --git a/arch/powerpc/kexec/crash.c b/arch/powerpc/kexec/crash.c index 0196d0c211ac..10f997e6bb95 100644 --- a/arch/powerpc/kexec/crash.c +++ b/arch/powerpc/kexec/crash.c @@ -105,8 +105,8 @@ void crash_ipi_callback(struct pt_regs *regs) static void crash_kexec_prepare_cpus(int cpu) { unsigned int msecs; - unsigned int ncpus = num_online_cpus() - 1;/* Excluding the panic cpu */ - int tries = 0; + volatile unsigned int ncpus = num_online_cpus() - 1;/* Excluding the panic cpu */ + volatile int tries = 0; int (*old_handler)(struct pt_regs *regs);printk(KERN_EMERG "Sending IPI to other CPUs\n");diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c index c8173e92f19d..ce0eacf77645 100644 --- a/arch/powerpc/xmon/xmon.c +++ b/arch/powerpc/xmon/xmon.c @@ -489,10 +489,10 @@ static void xmon_touch_watchdogs(void) touch_nmi_watchdog(); }-static int xmon_core(struct pt_regs *regs, int fromipi)+static int xmon_core(struct pt_regs *regs, volatile int fromipi) { - int cmd = 0; - struct bpt *bp; + volatile int cmd = 0; + struct bpt *volatile bp; long recurse_jmp[JMP_BUF_LEN]; bool locked_down; unsigned long offset; @@ -857,7 +857,7 @@ static inline void force_enable_xmon(void) static struct bpt *at_breakpoint(unsigned long pc) { int i; - struct bpt *bp; + struct bpt *volatile bp;bp = bpts;for (i = 0; i < NBPTS; ++i, ++bp) @@ -3005,7 +3005,7 @@ static void dump_opal_msglog(void) { unsigned char buf[128]; ssize_t res; - loff_t pos = 0; + volatile loff_t pos = 0;if (!firmware_has_feature(FW_FEATURE_OPAL)) {printf("Machine is not running OPAL firmware.\n"); @@ -3160,7 +3160,7 @@ memzcan(void) printf("%.8lx\n", a - mskip); }-static void show_task(struct task_struct *tsk)+static void show_task(struct task_struct *volatile tsk) { char state;@@ -3204,7 +3204,7 @@ static void format_pte(void *ptep, unsigned long pte)static void show_pte(unsigned long addr) { unsigned long tskv = 0; - struct task_struct *tsk = NULL; + struct task_struct *volatile tsk = NULL; struct mm_struct *mm; pgd_t *pgdp; p4d_t *p4dp; @@ -3299,7 +3299,7 @@ static void show_pte(unsigned long addr) static void show_tasks(void) { unsigned long tskv; - struct task_struct *tsk = NULL; + struct task_struct *volatile tsk = NULL;printf(" task_struct ->thread.ksp ->thread.regs PID PPID S P CMD\n"); @@ -3622,7 +3622,7 @@ static void xmon_print_symbol(unsigned long address, const char *mid,const char *after) { char *modname; - const char *name = NULL; + const char *volatile name = NULL; unsigned long offset, size;printf(REG, address);@@ -4054,7 +4054,7 @@ void xmon_register_spus(struct list_head *list) static void stop_spus(void) { struct spu *spu; - int i; + volatile int i; u64 tmp;for (i = 0; i < XMON_NUM_SPUS; i++) {@@ -4095,7 +4095,7 @@ static void stop_spus(void) static void restart_spus(void) { struct spu *spu; - int i; + volatile int i;for (i = 0; i < XMON_NUM_SPUS; i++) {if (!spu_info[i].spu)
