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[lldb] Don't use a vm addr range starting at 0 for local memory #100288

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Jul 25, 2024
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[lldb] Don't use a vm addr range starting at 0 for local memory #100288

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2843944
[lldb] Don't use a vm addr range starting at 0 for local memory
jasonmolenda Jul 24, 2024
6fbe759
fix minor nit.
jasonmolenda Jul 24, 2024
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8 changes: 7 additions & 1 deletion lldb/docs/resources/lldbgdbremote.md
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Original file line number Diff line number Diff line change
Expand Up @@ -1403,6 +1403,12 @@ For instance, with a macOS process which has nothing mapped in the first
The lack of `permissions:` indicates that none of read/write/execute are valid
for this region.

The stub must include `permissions:` key-value on all memory ranges
that are valid to access in the inferior process -- the lack of
`permissions:` means that this is an inaccessible (no page table
entries exist, in a system using VM) memory range. If a stub cannot
determine actual permissions, return `rwx`.

**Priority To Implement:** Medium

This is nice to have, but it isn't necessary. It helps LLDB
Expand Down Expand Up @@ -2434,4 +2440,4 @@ The `0x` prefixes are optional - like most of the gdb-remote packets,
omitting them will work fine; these numbers are always base 16.

The length of the payload is not provided. A reliable, 8-bit clean,
transport layer is assumed.
transport layer is assumed.
18 changes: 13 additions & 5 deletions lldb/source/Expression/IRMemoryMap.cpp
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Expand Up @@ -84,7 +84,7 @@ lldb::addr_t IRMemoryMap::FindSpace(size_t size) {
// any allocations. Otherwise start at the beginning of memory.

if (m_allocations.empty()) {
ret = 0x0;
ret = 0;
} else {
auto back = m_allocations.rbegin();
lldb::addr_t addr = back->first;
Expand Down Expand Up @@ -116,10 +116,18 @@ lldb::addr_t IRMemoryMap::FindSpace(size_t size) {
Status err = process_sp->GetMemoryRegionInfo(ret, region_info);
if (err.Success()) {
while (true) {
if (region_info.GetReadable() != MemoryRegionInfo::OptionalBool::eNo ||
region_info.GetWritable() != MemoryRegionInfo::OptionalBool::eNo ||
region_info.GetExecutable() !=
MemoryRegionInfo::OptionalBool::eNo) {
if (region_info.GetRange().GetRangeBase() == 0 &&
region_info.GetRange().GetRangeEnd() < end_of_memory) {
// Don't use a region that starts at address 0,
// it can make it harder to debug null dereference crashes
// in the inferior.
ret = region_info.GetRange().GetRangeEnd();
} else if (region_info.GetReadable() !=
MemoryRegionInfo::OptionalBool::eNo ||
region_info.GetWritable() !=
MemoryRegionInfo::OptionalBool::eNo ||
region_info.GetExecutable() !=
MemoryRegionInfo::OptionalBool::eNo) {
if (region_info.GetRange().GetRangeEnd() - 1 >= end_of_memory) {
ret = LLDB_INVALID_ADDRESS;
break;
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