The current brk() implementation does not de-allocate pages if a lower
address is given compared to earlier brk() calls.
But according to the manpage, brk() shall deallocate memory in this case
and currently it breaks a real-world application, specifically building
the debian gcl package in qemu-user.
Fix this issue by reworking the qemu brk() implementation.
Tested with the C-code testcase included in qemu commit 4d1de87c750, and
by building debian package of gcl in a hppa-linux guest on a x86-64
host.
Signed-off-by: Helge Deller <deller@gmx.de>
---
v3:
- Fixed one bug where page aligned address was returned instead
of requested address.
- Dropped debug info which is partly outdated now
- Reduced number of changed lines in diff compared to v2 to make
diff easier readable
- Fixed changelog of v2
v2:
- Fixed return value of brk(). The v1 version wrongly page-aligned
the provided address, while userspace expects an unmodified
address returned.
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 4fee882cd7..7d28802aa6 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -838,49 +838,52 @@ static inline int host_to_target_sock_type(int host_type)
}
static abi_ulong target_brk;
-static abi_ulong target_original_brk;
static abi_ulong brk_page;
void target_set_brk(abi_ulong new_brk)
{
- target_original_brk = target_brk = HOST_PAGE_ALIGN(new_brk);
+ target_brk = new_brk;
brk_page = HOST_PAGE_ALIGN(target_brk);
}
-//#define DEBUGF_BRK(message, args...) do { fprintf(stderr, (message), ## args); } while (0)
-#define DEBUGF_BRK(message, args...)
-
/* do_brk() must return target values and target errnos. */
-abi_long do_brk(abi_ulong new_brk)
+abi_long do_brk(abi_ulong brk_val)
{
abi_long mapped_addr;
abi_ulong new_alloc_size;
+ abi_ulong new_brk, new_host_brk_page;
/* brk pointers are always untagged */
- DEBUGF_BRK("do_brk(" TARGET_ABI_FMT_lx ") -> ", new_brk);
-
- if (!new_brk) {
- DEBUGF_BRK(TARGET_ABI_FMT_lx " (!new_brk)\n", target_brk);
+ /* return old brk value if brk_val unchanged or zero */
+ if (!brk_val || brk_val == target_brk) {
return target_brk;
}
- if (new_brk < target_original_brk) {
- DEBUGF_BRK(TARGET_ABI_FMT_lx " (new_brk < target_original_brk)\n",
- target_brk);
+
+ new_brk = TARGET_PAGE_ALIGN(brk_val);
+ new_host_brk_page = HOST_PAGE_ALIGN(brk_val);
+
+ /* brk_val and old target_brk might be on the same page */
+ if (new_brk == TARGET_PAGE_ALIGN(target_brk)) {
+ if (brk_val > target_brk) {
+ /* empty remaining bytes in (possibly larger) host page */
+ memset(g2h_untagged(target_brk), 0, new_host_brk_page - target_brk);
+ }
+ target_brk = brk_val;
return target_brk;
}
- /* If the new brk is less than the highest page reserved to the
- * target heap allocation, set it and we're almost done... */
- if (new_brk <= brk_page) {
- /* Heap contents are initialized to zero, as for anonymous
- * mapped pages. */
- if (new_brk > target_brk) {
- memset(g2h_untagged(target_brk), 0, new_brk - target_brk);
- }
- target_brk = new_brk;
- DEBUGF_BRK(TARGET_ABI_FMT_lx " (new_brk <= brk_page)\n", target_brk);
- return target_brk;
+ /* Release heap if necesary */
+ if (new_brk < target_brk) {
+ /* empty remaining bytes in (possibly larger) host page */
+ memset(g2h_untagged(brk_val), 0, new_host_brk_page - brk_val);
+
+ /* free unused host pages and set new brk_page */
+ target_munmap(new_host_brk_page, brk_page - new_host_brk_page);
+ brk_page = new_host_brk_page;
+
+ target_brk = brk_val;
+ return target_brk;
}
/* We need to allocate more memory after the brk... Note that
@@ -889,10 +892,14 @@ abi_long do_brk(abi_ulong new_brk)
* itself); instead we treat "mapped but at wrong address" as
* a failure and unmap again.
*/
- new_alloc_size = HOST_PAGE_ALIGN(new_brk - brk_page);
- mapped_addr = get_errno(target_mmap(brk_page, new_alloc_size,
+ new_alloc_size = new_host_brk_page - brk_page;
+ if (new_alloc_size) {
+ mapped_addr = get_errno(target_mmap(brk_page, new_alloc_size,
PROT_READ|PROT_WRITE,
MAP_ANON|MAP_PRIVATE, 0, 0));
+ } else {
+ mapped_addr = brk_page;
+ }
if (mapped_addr == brk_page) {
/* Heap contents are initialized to zero, as for anonymous
@@ -904,10 +911,8 @@ abi_long do_brk(abi_ulong new_brk)
* then shrunken). */
memset(g2h_untagged(target_brk), 0, brk_page - target_brk);
- target_brk = new_brk;
- brk_page = HOST_PAGE_ALIGN(target_brk);
- DEBUGF_BRK(TARGET_ABI_FMT_lx " (mapped_addr == brk_page)\n",
- target_brk);
+ target_brk = brk_val;
+ brk_page = new_host_brk_page;
return target_brk;
} else if (mapped_addr != -1) {
/* Mapped but at wrong address, meaning there wasn't actually
@@ -915,10 +920,6 @@ abi_long do_brk(abi_ulong new_brk)
*/
target_munmap(mapped_addr, new_alloc_size);
mapped_addr = -1;
- DEBUGF_BRK(TARGET_ABI_FMT_lx " (mapped_addr != -1)\n", target_brk);
- }
- else {
- DEBUGF_BRK(TARGET_ABI_FMT_lx " (otherwise)\n", target_brk);
}
#if defined(TARGET_ALPHA)
Le 25/12/2022 à 09:23, Helge Deller a écrit : > The current brk() implementation does not de-allocate pages if a lower > address is given compared to earlier brk() calls. > But according to the manpage, brk() shall deallocate memory in this case > and currently it breaks a real-world application, specifically building > the debian gcl package in qemu-user. > > Fix this issue by reworking the qemu brk() implementation. > > Tested with the C-code testcase included in qemu commit 4d1de87c750, and > by building debian package of gcl in a hppa-linux guest on a x86-64 > host. > > Signed-off-by: Helge Deller <deller@gmx.de> > > --- > v3: > - Fixed one bug where page aligned address was returned instead > of requested address. > - Dropped debug info which is partly outdated now > - Reduced number of changed lines in diff compared to v2 to make > diff easier readable > - Fixed changelog of v2 > v2: > - Fixed return value of brk(). The v1 version wrongly page-aligned > the provided address, while userspace expects an unmodified > address returned. > > > diff --git a/linux-user/syscall.c b/linux-user/syscall.c > index 4fee882cd7..7d28802aa6 100644 > --- a/linux-user/syscall.c > +++ b/linux-user/syscall.c > @@ -838,49 +838,52 @@ static inline int host_to_target_sock_type(int host_type) > } > > static abi_ulong target_brk; > -static abi_ulong target_original_brk; > static abi_ulong brk_page; > > void target_set_brk(abi_ulong new_brk) > { > - target_original_brk = target_brk = HOST_PAGE_ALIGN(new_brk); > + target_brk = new_brk; > brk_page = HOST_PAGE_ALIGN(target_brk); > } > > -//#define DEBUGF_BRK(message, args...) do { fprintf(stderr, (message), ## args); } while (0) > -#define DEBUGF_BRK(message, args...) > - > /* do_brk() must return target values and target errnos. */ > -abi_long do_brk(abi_ulong new_brk) > +abi_long do_brk(abi_ulong brk_val) > { > abi_long mapped_addr; > abi_ulong new_alloc_size; > + abi_ulong new_brk, new_host_brk_page; > > /* brk pointers are always untagged */ > > - DEBUGF_BRK("do_brk(" TARGET_ABI_FMT_lx ") -> ", new_brk); > - > - if (!new_brk) { > - DEBUGF_BRK(TARGET_ABI_FMT_lx " (!new_brk)\n", target_brk); > + /* return old brk value if brk_val unchanged or zero */ > + if (!brk_val || brk_val == target_brk) { > return target_brk; > } > - if (new_brk < target_original_brk) { > - DEBUGF_BRK(TARGET_ABI_FMT_lx " (new_brk < target_original_brk)\n", > - target_brk); > + > + new_brk = TARGET_PAGE_ALIGN(brk_val); > + new_host_brk_page = HOST_PAGE_ALIGN(brk_val); > + > + /* brk_val and old target_brk might be on the same page */ > + if (new_brk == TARGET_PAGE_ALIGN(target_brk)) { > + if (brk_val > target_brk) { > + /* empty remaining bytes in (possibly larger) host page */ > + memset(g2h_untagged(target_brk), 0, new_host_brk_page - target_brk); > + } > + target_brk = brk_val; > return target_brk; > } > > - /* If the new brk is less than the highest page reserved to the > - * target heap allocation, set it and we're almost done... */ > - if (new_brk <= brk_page) { > - /* Heap contents are initialized to zero, as for anonymous > - * mapped pages. */ > - if (new_brk > target_brk) { > - memset(g2h_untagged(target_brk), 0, new_brk - target_brk); > - } > - target_brk = new_brk; > - DEBUGF_BRK(TARGET_ABI_FMT_lx " (new_brk <= brk_page)\n", target_brk); > - return target_brk; > + /* Release heap if necesary */ > + if (new_brk < target_brk) { > + /* empty remaining bytes in (possibly larger) host page */ > + memset(g2h_untagged(brk_val), 0, new_host_brk_page - brk_val); > + > + /* free unused host pages and set new brk_page */ > + target_munmap(new_host_brk_page, brk_page - new_host_brk_page); > + brk_page = new_host_brk_page; > + > + target_brk = brk_val; > + return target_brk; > } > > /* We need to allocate more memory after the brk... Note that > @@ -889,10 +892,14 @@ abi_long do_brk(abi_ulong new_brk) > * itself); instead we treat "mapped but at wrong address" as > * a failure and unmap again. > */ > - new_alloc_size = HOST_PAGE_ALIGN(new_brk - brk_page); > - mapped_addr = get_errno(target_mmap(brk_page, new_alloc_size, > + new_alloc_size = new_host_brk_page - brk_page; > + if (new_alloc_size) { > + mapped_addr = get_errno(target_mmap(brk_page, new_alloc_size, > PROT_READ|PROT_WRITE, > MAP_ANON|MAP_PRIVATE, 0, 0)); > + } else { > + mapped_addr = brk_page; > + } > > if (mapped_addr == brk_page) { > /* Heap contents are initialized to zero, as for anonymous > @@ -904,10 +911,8 @@ abi_long do_brk(abi_ulong new_brk) > * then shrunken). */ > memset(g2h_untagged(target_brk), 0, brk_page - target_brk); > > - target_brk = new_brk; > - brk_page = HOST_PAGE_ALIGN(target_brk); > - DEBUGF_BRK(TARGET_ABI_FMT_lx " (mapped_addr == brk_page)\n", > - target_brk); > + target_brk = brk_val; > + brk_page = new_host_brk_page; > return target_brk; > } else if (mapped_addr != -1) { > /* Mapped but at wrong address, meaning there wasn't actually > @@ -915,10 +920,6 @@ abi_long do_brk(abi_ulong new_brk) > */ > target_munmap(mapped_addr, new_alloc_size); > mapped_addr = -1; > - DEBUGF_BRK(TARGET_ABI_FMT_lx " (mapped_addr != -1)\n", target_brk); > - } > - else { > - DEBUGF_BRK(TARGET_ABI_FMT_lx " (otherwise)\n", target_brk); > } > > #if defined(TARGET_ALPHA) > Applied to my linux-user-for-8.0 branch. Thanks, Laurent
© 2016 - 2024 Red Hat, Inc.