[ccan] [PATCH] altstack: stack alignment and accounting tweaks
David Gibson
david at gibson.dropbear.id.au
Wed Feb 3 17:16:48 AEDT 2016
On Mon, Feb 01, 2016 at 02:43:16AM +0000, Dan Good wrote:
>
> * add altstack_remn, returns amount of stack remaining
> * increase mapping by 1 page to handle abutment case
> * capture rsp earlier
> * align stack to 16 bytes
>
> Signed-off-by: Dan Good <dan at dancancode.com>
Bit of a messy bitser, but doesn't look it will make anything
worse. so go ahead and push.
Unfortunately, altstack is breaking travis builds at the moment (see,
e.g. https://travis-ci.org/dgibson/ccan/jobs/106661592) - but not
local builds for me which is making it difficult to debug.
Some investigation showed that the test prog was getting a SIGBUS, but
I didn't get further than that.
altstack also breaks "make all" on any non-x86_64 platform (including
32-bit x86) which is pretty horrid. For that I think we need to
adjust the makefiles to look at rusty's new "ported" stuff from _info.
> ---
> ccan/altstack/altstack.c | 17 ++++++++++++++---
> ccan/altstack/altstack.h | 14 ++++++++++++++
> ccan/altstack/test/run.c | 20 +++++++++++++-------
> 3 files changed, 41 insertions(+), 10 deletions(-)
>
> diff --git a/ccan/altstack/altstack.c b/ccan/altstack/altstack.c
> index 6faf38f..b71c64f 100644
> --- a/ccan/altstack/altstack.c
> +++ b/ccan/altstack/altstack.c
> @@ -8,6 +8,7 @@
> #include <signal.h>
> #include <stdio.h>
> #include <string.h>
> +#include <unistd.h>
> #include <sys/mman.h>
>
> static __thread char ebuf[ALTSTACK_ERR_MAXLEN];
> @@ -37,6 +38,11 @@ static void segvjmp(int signum)
> }
>
> static __thread void *rsp_save_[2];
> +static __thread rlim_t max_;
> +
> +rlim_t altstack_max(void) {
> + return max_;
> +}
>
> static ptrdiff_t rsp_save(unsigned i) {
> assert(i < 2);
> @@ -57,6 +63,7 @@ static __thread void *arg_, *out_;
>
> int altstack(rlim_t max, void *(*fn)(void *), void *arg, void **out)
> {
> + long pgsz = sysconf(_SC_PAGESIZE);
> int ret = -1, undo = 0;
> char *m;
> struct rlimit rl_save;
> @@ -69,11 +76,16 @@ int altstack(rlim_t max, void *(*fn)(void *), void *arg, void **out)
> fn_ = fn;
> arg_ = arg;
> out_ = 0;
> + max_ = max;
> ebuf[elen = 0] = '\0';
> if (out) *out = 0;
>
> + // if the first page below the mapping is in use, we get max-pgsz usable bytes
> + // add pgsz to max to guarantee at least max usable bytes
> + max += pgsz;
> +
> ok(getrlimit(RLIMIT_STACK, &rl_save), 1);
> - ok(setrlimit(RLIMIT_STACK, &(struct rlimit) { max, rl_save.rlim_max }), 1);
> + ok(setrlimit(RLIMIT_STACK, &(struct rlimit) { max_, rl_save.rlim_max }), 1);
> undo++;
>
> ok(m = mmap(0, max, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_GROWSDOWN|MAP_NORESERVE, -1, 0), 1);
> @@ -91,8 +103,7 @@ int altstack(rlim_t max, void *(*fn)(void *), void *arg, void **out)
> ok(sigaction(SIGSEGV, &sa, &sa_save), 1);
> undo++;
>
> - asm volatile ("movq %%rsp, %%r10\nmov %0, %%rsp\npush %%r10" : : "g" (m + max) : "r10");
> - rsp_save(0);
> + asm volatile ("movq %%rsp, %%r10\nmov %1, %%rsp\nmov %%rsp, %0\nsub $8, %%rsp\npush %%r10" : "=g" (rsp_save_[0]) : "g" (m + max) : "r10");
> out_ = fn_(arg_);
> asm volatile ("pop %rsp");
> ret = 0;
> diff --git a/ccan/altstack/altstack.h b/ccan/altstack/altstack.h
> index 5570e7b..4445a2a 100644
> --- a/ccan/altstack/altstack.h
> +++ b/ccan/altstack/altstack.h
> @@ -104,6 +104,20 @@ char *altstack_geterr(void);
> ptrdiff_t altstack_used(void);
>
> /**
> + * altstack_max - return usable stack size
> + *
> + * Returns: max value from altstack() call
> + */
> +rlim_t altstack_max(void);
> +
> +/**
> + * altstack_remn - return amount of stack remaining
> + *
> + * Returns: altstack_max() minus altstack_used()
> + */
> +#define altstack_remn() (altstack_max() - altstack_used())
> +
> +/**
> * altstack_rsp_save - set initial rsp value
> *
> * Capture the current value of rsp for future altstack_used()
> diff --git a/ccan/altstack/test/run.c b/ccan/altstack/test/run.c
> index adc1020..d0b8d28 100644
> --- a/ccan/altstack/test/run.c
> +++ b/ccan/altstack/test/run.c
> @@ -4,6 +4,7 @@
> #include <setjmp.h>
> #include <signal.h>
> #include <string.h>
> +#include <unistd.h>
> #include <sys/mman.h>
> #include <ccan/tap/tap.h>
> #include <ccan/altstack/altstack.h>
> @@ -20,13 +21,13 @@ enum {
> };
> int fail, call1, call2;
> char *m_;
> -rlim_t max_;
> +rlim_t msz_;
> #define e(x) (900+(x))
> #define seterr(x) (errno = e(x))
> #define setcall(x) ((call1 |= !errno ? (x) : 0), (call2 |= errno || out_ ? (x) : 0))
> #define getrlimit(...) (fail&getrlimit_ ? (seterr(getrlimit_), -1) : (setcall(getrlimit_), getrlimit(__VA_ARGS__)))
> #define mmap(...) (fail&mmap_ ? (seterr(mmap_), (void *)-1) : (setcall(mmap_), mmap(__VA_ARGS__)))
> -#define munmap(a, b) (fail&munmap_ ? (seterr(munmap_), -1) : (setcall(munmap_), munmap(m_=(a), max_=(b))))
> +#define munmap(a, b) (fail&munmap_ ? (seterr(munmap_), -1) : (setcall(munmap_), munmap(m_=(a), msz_=(b))))
> #define setrlimit(...) (fail&setrlimit_ ? (seterr(setrlimit_), -1) : (setcall(setrlimit_), setrlimit(__VA_ARGS__)))
> #define sigaltstack(...) (fail&sigaltstack_ ? (seterr(sigaltstack_), -1) : (setcall(sigaltstack_), sigaltstack(__VA_ARGS__)))
> #define sigaction(...) (fail&sigaction_ ? (seterr(sigaction_), -1) : (setcall(sigaction_), sigaction(__VA_ARGS__)))
> @@ -58,7 +59,9 @@ static void *wrap(void *i)
>
> int main(void)
> {
> - plan_tests(16);
> + long pgsz = sysconf(_SC_PAGESIZE);
> +
> + plan_tests(17);
>
> #define chkfail(x, y, z, c1, c2) (call1 = 0, call2 = 0, errno = 0, ok1((fail = x) && (y) && errno == (z) && call1 == (c1) && call2 == (c2)));
> #define chkok( y, z, c1, c2) (call1 = 0, call2 = 0, errno = 0, fail = 0, ok1((y) && errno == (z) && call1 == (c1) && call2 == (c2)));
> @@ -86,7 +89,7 @@ int main(void)
> chkfail(munmap_, altstack(8*MiB, wrap, 0, 0) == 1, e(munmap_),
> getrlimit_|setrlimit_|mmap_|sigaltstack_|sigaction_,
> setrlimit_|sigaltstack_|sigaction_);
> - if (fail = 0, munmap(m_, max_) == -1)
> + if (fail = 0, munmap(m_, msz_) == -1)
> err(1, "munmap");
>
> chkok( altstack(1*MiB, wrap, (void *) 1000000, 0) == -1, EOVERFLOW,
> @@ -102,10 +105,12 @@ int main(void)
> chkfail(munmap_, altstack(1*MiB, wrap, (void *) 1000000, 0) == -1, EOVERFLOW,
> getrlimit_|setrlimit_|mmap_|sigaltstack_|sigaction_,
> setrlimit_|sigaltstack_|sigaction_);
> - if (fail = 0, munmap(m_, max_) == -1)
> + if (fail = 0, munmap(m_, msz_) == -1)
> err(1, "munmap");
>
> - ok1(used > 1*MiB-1*KiB && used < 1*MiB);
> + ok1(altstack_max() == 1*MiB);
> + diag("used: %lu", used);
> + ok1(used >= 1*MiB && used <= 1*MiB + pgsz);
>
> char *p;
> for(p = altstack_geterr(); *p; p++)
> @@ -128,7 +133,8 @@ int main(void)
> getrlimit_|setrlimit_|mmap_|sigaltstack_|sigaction_,
> setrlimit_|munmap_|sigaltstack_|sigaction_);
>
> - ok1(used > 8*MiB-8*KiB && used < 8*MiB);
> + diag("used: %lu", used);
> + ok1(used >= 8*MiB && used <= 8*MiB + pgsz);
>
> used = 0;
> chkok( altstack(8*MiB, wrap, (void *) 100000, 0) == 0, 0,
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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