Dump memory going from unreadable to readable.
If the first read when dumping memory returns no data, skip ahead to
the next page boundary and try and read from there. This fixes a case
where the address at which to start dumping memory is unreadable, but
crosses back into readable memory.
Bug: 22234753
Change-Id: Ie28d5c027013577ca06f5396aba498366a3b6749
diff --git a/debuggerd/utility.cpp b/debuggerd/utility.cpp
index 545a572..f5d6ec1 100644
--- a/debuggerd/utility.cpp
+++ b/debuggerd/utility.cpp
@@ -156,13 +156,28 @@
bytes &= ~(sizeof(uintptr_t) - 1);
}
- if (bytes < MEMORY_BYTES_TO_DUMP && bytes > 0) {
- // Try to do one more read. This could happen if a read crosses a map, but
- // the maps do not have any break between them. Only requires one extra
- // read because a map has to contain at least one page, and the total
- // number of bytes to dump is smaller than a page.
- size_t bytes2 = backtrace->Read(addr + bytes, reinterpret_cast<uint8_t*>(data) + bytes,
- sizeof(data) - bytes);
+ uintptr_t start = 0;
+ bool skip_2nd_read = false;
+ if (bytes == 0) {
+ // In this case, we might want to try another read at the beginning of
+ // the next page only if it's within the amount of memory we would have
+ // read.
+ size_t page_size = sysconf(_SC_PAGE_SIZE);
+ start = ((addr + (page_size - 1)) & ~(page_size - 1)) - addr;
+ if (start == 0 || start >= MEMORY_BYTES_TO_DUMP) {
+ skip_2nd_read = true;
+ }
+ }
+
+ if (bytes < MEMORY_BYTES_TO_DUMP && !skip_2nd_read) {
+ // Try to do one more read. This could happen if a read crosses a map,
+ // but the maps do not have any break between them. Or it could happen
+ // if reading from an unreadable map, but the read would cross back
+ // into a readable map. Only requires one extra read because a map has
+ // to contain at least one page, and the total number of bytes to dump
+ // is smaller than a page.
+ size_t bytes2 = backtrace->Read(addr + start + bytes, reinterpret_cast<uint8_t*>(data) + bytes,
+ sizeof(data) - bytes - start);
bytes += bytes2;
if (bytes2 > 0 && bytes % sizeof(uintptr_t) != 0) {
// This should never happen, but we'll try and continue any way.
@@ -178,15 +193,16 @@
// On 32-bit machines, there are still 16 bytes per line but addresses and
// words are of course presented differently.
uintptr_t* data_ptr = data;
+ size_t current = 0;
+ size_t total_bytes = start + bytes;
for (size_t line = 0; line < MEMORY_BYTES_TO_DUMP / MEMORY_BYTES_PER_LINE; line++) {
std::string logline;
android::base::StringAppendF(&logline, " %" PRIPTR, addr);
addr += MEMORY_BYTES_PER_LINE;
std::string ascii;
- for (size_t i = 0; i < MEMORY_BYTES_PER_LINE / sizeof(uintptr_t); i++, data_ptr++) {
- if (bytes >= sizeof(uintptr_t)) {
- bytes -= sizeof(uintptr_t);
+ for (size_t i = 0; i < MEMORY_BYTES_PER_LINE / sizeof(uintptr_t); i++) {
+ if (current >= start && current + sizeof(uintptr_t) <= total_bytes) {
android::base::StringAppendF(&logline, " %" PRIPTR, *data_ptr);
// Fill out the ascii string from the data.
@@ -198,10 +214,12 @@
ascii += '.';
}
}
+ data_ptr++;
} else {
logline += ' ' + std::string(sizeof(uintptr_t) * 2, '-');
ascii += std::string(sizeof(uintptr_t), '.');
}
+ current += sizeof(uintptr_t);
}
_LOG(log, logtype::MEMORY, "%s %s\n", logline.c_str(), ascii.c_str());
}