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linux-user: Fix brk() to release pages

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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 4d1de87c75, 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>
Message-Id: <Y6gId80ek49TK1xB@p100>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
This commit is contained in:
Helge Deller 2022-12-25 09:23:19 +01:00 committed by Laurent Vivier
parent 25bb27c715
commit 86f04735ac
1 changed files with 36 additions and 35 deletions
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67
linux-user/syscall.c
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@ -795,48 +795,51 @@ static inline int host_to_target_sock_type(int host_type)
} }
static abi_ulong target_brk; static abi_ulong target_brk;
static abi_ulong target_original_brk;
static abi_ulong brk_page; static abi_ulong brk_page;
void target_set_brk(abi_ulong new_brk) 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); 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. */ /* 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_long mapped_addr;
abi_ulong new_alloc_size; abi_ulong new_alloc_size;
abi_ulong new_brk, new_host_brk_page;
/* brk pointers are always untagged */ /* brk pointers are always untagged */
DEBUGF_BRK("do_brk(" TARGET_ABI_FMT_lx ") -> ", new_brk); /* return old brk value if brk_val unchanged or zero */
if (!brk_val || brk_val == target_brk) {
if (!new_brk) {
DEBUGF_BRK(TARGET_ABI_FMT_lx " (!new_brk)\n", 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);
return target_brk; return target_brk;
} }
/* If the new brk is less than the highest page reserved to the new_brk = TARGET_PAGE_ALIGN(brk_val);
* target heap allocation, set it and we're almost done... */ new_host_brk_page = HOST_PAGE_ALIGN(brk_val);
if (new_brk <= brk_page) {
/* Heap contents are initialized to zero, as for anonymous /* brk_val and old target_brk might be on the same page */
* mapped pages. */ if (new_brk == TARGET_PAGE_ALIGN(target_brk)) {
if (new_brk > target_brk) { if (brk_val > target_brk) {
memset(g2h_untagged(target_brk), 0, new_brk - target_brk); /* empty remaining bytes in (possibly larger) host page */
memset(g2h_untagged(target_brk), 0, new_host_brk_page - target_brk);
} }
target_brk = new_brk; target_brk = brk_val;
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; return target_brk;
} }
@ -846,10 +849,14 @@ abi_long do_brk(abi_ulong new_brk)
* itself); instead we treat "mapped but at wrong address" as * itself); instead we treat "mapped but at wrong address" as
* a failure and unmap again. * a failure and unmap again.
*/ */
new_alloc_size = HOST_PAGE_ALIGN(new_brk - brk_page); new_alloc_size = new_host_brk_page - brk_page;
if (new_alloc_size) {
mapped_addr = get_errno(target_mmap(brk_page, new_alloc_size, mapped_addr = get_errno(target_mmap(brk_page, new_alloc_size,
PROT_READ|PROT_WRITE, PROT_READ|PROT_WRITE,
MAP_ANON|MAP_PRIVATE, 0, 0)); MAP_ANON|MAP_PRIVATE, 0, 0));
} else {
mapped_addr = brk_page;
}
if (mapped_addr == brk_page) { if (mapped_addr == brk_page) {
/* Heap contents are initialized to zero, as for anonymous /* Heap contents are initialized to zero, as for anonymous
@ -861,10 +868,8 @@ abi_long do_brk(abi_ulong new_brk)
* then shrunken). */ * then shrunken). */
memset(g2h_untagged(target_brk), 0, brk_page - target_brk); memset(g2h_untagged(target_brk), 0, brk_page - target_brk);
target_brk = new_brk; target_brk = brk_val;
brk_page = HOST_PAGE_ALIGN(target_brk); brk_page = new_host_brk_page;
DEBUGF_BRK(TARGET_ABI_FMT_lx " (mapped_addr == brk_page)\n",
target_brk);
return target_brk; return target_brk;
} else if (mapped_addr != -1) { } else if (mapped_addr != -1) {
/* Mapped but at wrong address, meaning there wasn't actually /* Mapped but at wrong address, meaning there wasn't actually
@ -872,10 +877,6 @@ abi_long do_brk(abi_ulong new_brk)
*/ */
target_munmap(mapped_addr, new_alloc_size); target_munmap(mapped_addr, new_alloc_size);
mapped_addr = -1; 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) #if defined(TARGET_ALPHA)