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[Qemu-devel] [PATCH] memory: use signed arithmetic
From: |
Avi Kivity |
Subject: |
[Qemu-devel] [PATCH] memory: use signed arithmetic |
Date: |
Tue, 2 Aug 2011 23:50:49 +0300 |
When trying to map an alias of a ram region, where the alias starts at
address A and we map it into address B, and A > B, we had an arithmetic
underflow. Because we use unsigned arithmetic, the underflow converted
into a large number which failed addrrange_intersects() tests.
The concrete example which triggered this was cirrus vga mapping
the framebuffer at offsets 0xc0000-0xc7fff (relative to the start of
the framebuffer) into offsets 0xa0000 (relative to system addres space
start).
With our favorite analogy of a windowing system, this is equivalent to
dragging a subwindow off the left edge of the screen, and failing to clip
it into its parent window which is on screen.
Fix by switching to signed arithmetic.
Signed-off-by: Avi Kivity <address@hidden>
---
exec.c | 2 +-
memory.c | 18 +++++++++---------
2 files changed, 10 insertions(+), 10 deletions(-)
diff --git a/exec.c b/exec.c
index 476b507..751fd89 100644
--- a/exec.c
+++ b/exec.c
@@ -3818,7 +3818,7 @@ static void io_mem_init(void)
static void memory_map_init(void)
{
system_memory = qemu_malloc(sizeof(*system_memory));
- memory_region_init(system_memory, "system", UINT64_MAX);
+ memory_region_init(system_memory, "system", INT64_MAX);
set_system_memory_map(system_memory);
}
diff --git a/memory.c b/memory.c
index 5f20320..8ef6497 100644
--- a/memory.c
+++ b/memory.c
@@ -23,11 +23,11 @@ unsigned memory_region_transaction_depth = 0;
typedef struct AddrRange AddrRange;
struct AddrRange {
- uint64_t start;
- uint64_t size;
+ int64_t start;
+ int64_t size;
};
-static AddrRange addrrange_make(uint64_t start, uint64_t size)
+static AddrRange addrrange_make(int64_t start, int64_t size)
{
return (AddrRange) { start, size };
}
@@ -37,7 +37,7 @@ static bool addrrange_equal(AddrRange r1, AddrRange r2)
return r1.start == r2.start && r1.size == r2.size;
}
-static uint64_t addrrange_end(AddrRange r)
+static int64_t addrrange_end(AddrRange r)
{
return r.start + r.size;
}
@@ -56,9 +56,9 @@ static bool addrrange_intersects(AddrRange r1, AddrRange r2)
static AddrRange addrrange_intersection(AddrRange r1, AddrRange r2)
{
- uint64_t start = MAX(r1.start, r2.start);
+ int64_t start = MAX(r1.start, r2.start);
/* off-by-one arithmetic to prevent overflow */
- uint64_t end = MIN(addrrange_end(r1) - 1, addrrange_end(r2) - 1);
+ int64_t end = MIN(addrrange_end(r1) - 1, addrrange_end(r2) - 1);
return addrrange_make(start, end - start + 1);
}
@@ -411,8 +411,8 @@ static void render_memory_region(FlatView *view,
MemoryRegion *subregion;
unsigned i;
target_phys_addr_t offset_in_region;
- uint64_t remain;
- uint64_t now;
+ int64_t remain;
+ int64_t now;
FlatRange fr;
AddrRange tmp;
@@ -486,7 +486,7 @@ static FlatView generate_memory_topology(MemoryRegion *mr)
flatview_init(&view);
- render_memory_region(&view, mr, 0, addrrange_make(0, UINT64_MAX));
+ render_memory_region(&view, mr, 0, addrrange_make(0, INT64_MAX));
flatview_simplify(&view);
return view;
--
1.7.5.3
- [Qemu-devel] [PATCH] memory: use signed arithmetic,
Avi Kivity <=