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Change the dyld notification function that lldb puts a breakpoint in
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On Darwin systems, the dynamic linker dyld has an empty function
it calls when binaries are added/removed from the process.  lldb puts
a breakpoint on this dyld function to catch the notifications.  The
function arguments are used by lldb to tell what is happening.

The linker has a natural representation when the addresses of
binaries being added/removed are in the pointer size of the process.
There is then a second function where the addresses of the binaries
are in a uint64_t array, which the debugger has been using before -
dyld allocates memory for the array, copies the values in to it,
and calls it for lldb's benefit.

This changes to using the native notifier function, with pointer-sized
addresses.

Differential Revision: https://reviews.llvm.org/D139453
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@jasonmolenda
jasonmolenda committed Jul 1, 2023
1 parent 2a631a8 commit 624813a
Showing 1 changed file with 52 additions and 15 deletions.
67 changes: 52 additions & 15 deletions lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderMacOS.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -235,10 +235,15 @@ bool DynamicLoaderMacOS::NotifyBreakpointHit(void *baton,
lldb::user_id_t break_loc_id) {
// Let the event know that the images have changed
// DYLD passes three arguments to the notification breakpoint.
// Arg1: enum dyld_notify_mode mode - 0 = adding, 1 = removing, 2 = remove
// all Arg2: unsigned long icount - Number of shared libraries
// added/removed Arg3: uint64_t mach_headers[] - Array of load addresses
// of binaries added/removed
//
// Arg1: enum dyld_notify_mode mode
// 0 = adding, 1 = removing, 2 = remove all, 3 = dyld moved
//
// Arg2: unsigned long count
// Number of shared libraries added/removed
//
// Arg3: struct dyld_image_info mach_headers[]
// Array of load addresses of binaries added/removed

DynamicLoaderMacOS *dyld_instance = (DynamicLoaderMacOS *)baton;

Expand Down Expand Up @@ -268,9 +273,10 @@ bool DynamicLoaderMacOS::NotifyBreakpointHit(void *baton,
ValueList argument_values;

Value mode_value; // enum dyld_notify_mode { dyld_notify_adding=0,
// dyld_notify_removing=1, dyld_notify_remove_all=2 };
// dyld_notify_removing=1, dyld_notify_remove_all=2,
// dyld_notify_dyld_moved=3 };
Value count_value; // unsigned long count
Value headers_value; // uint64_t machHeaders[] (aka void*)
Value headers_value; // struct dyld_image_info machHeaders[]

CompilerType clang_void_ptr_type =
scratch_ts_sp->GetBasicType(eBasicTypeVoid).GetPointerType();
Expand Down Expand Up @@ -299,6 +305,9 @@ bool DynamicLoaderMacOS::NotifyBreakpointHit(void *baton,
argument_values.PushValue(count_value);
argument_values.PushValue(headers_value);

// void lldb_image_notifier(enum dyld_image_mode mode, uint32_t infoCount,
// const dyld_image_info info[])

if (abi->GetArgumentValues(exe_ctx.GetThreadRef(), argument_values)) {
uint32_t dyld_mode =
argument_values.GetValueAtIndex(0)->GetScalar().UInt(-1);
Expand All @@ -312,12 +321,32 @@ bool DynamicLoaderMacOS::NotifyBreakpointHit(void *baton,
argument_values.GetValueAtIndex(2)->GetScalar().ULongLong(-1);
if (header_array != static_cast<uint64_t>(-1)) {
std::vector<addr_t> image_load_addresses;

// struct dyld_image_info_32 {
// uint32_t imageLoadAddress;
// uint32_t imageFilePath;
// uint32_t imageFileModDate;
// };
// struct dyld_image_info_64 {
// uint64_t imageLoadAddress;
// uint64_t imageFilePath;
// uint64_t imageFileModDate;
// };

uint32_t addr_size =
process->GetTarget().GetArchitecture().GetAddressByteSize();
for (uint64_t i = 0; i < image_infos_count; i++) {
Status error;
addr_t addr = process->ReadUnsignedIntegerFromMemory(
header_array + (8 * i), 8, LLDB_INVALID_ADDRESS, error);
if (addr != LLDB_INVALID_ADDRESS) {
addr_t dyld_image_info = header_array + (3 * addr_size * i);
addr_t addr =
process->ReadPointerFromMemory(dyld_image_info, error);
if (error.Success()) {
image_load_addresses.push_back(addr);
} else {
Debugger::ReportWarning(
"DynamicLoaderMacOS::NotifyBreakpointHit unable "
"to read binary mach-o load address at 0x%" PRIx64,
addr);
}
}
if (dyld_mode == 0) {
Expand Down Expand Up @@ -362,10 +391,18 @@ bool DynamicLoaderMacOS::NotifyBreakpointHit(void *baton,
Status error;
addr_t notification_addr =
process->ReadPointerFromMemory(notification_location, error);
if (ABISP abi_sp = process->GetABI())
notification_addr = abi_sp->FixCodeAddress(notification_addr);
if (!error.Success()) {
Debugger::ReportWarning(
"DynamicLoaderMacOS::NotifyBreakpointHit unable "
"to read address of dyld-handover notification function at "
"0x%" PRIx64,
notification_location);
} else {
if (ABISP abi_sp = process->GetABI())
notification_addr = abi_sp->FixCodeAddress(notification_addr);

dyld_instance->SetDYLDHandoverBreakpoint(notification_addr);
dyld_instance->SetDYLDHandoverBreakpoint(notification_addr);
}
}
}
}
Expand Down Expand Up @@ -431,9 +468,9 @@ bool DynamicLoaderMacOS::SetNotificationBreakpoint() {
Breakpoint *breakpoint =
m_process->GetTarget()
.CreateBreakpoint(&dyld_filelist, source_files,
"_dyld_debugger_notification",
eFunctionNameTypeFull, eLanguageTypeC, 0,
skip_prologue, internal, hardware)
"lldb_image_notifier", eFunctionNameTypeFull,
eLanguageTypeC, 0, skip_prologue, internal,
hardware)
.get();
breakpoint->SetCallback(DynamicLoaderMacOS::NotifyBreakpointHit, this,
true);
Expand Down

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