[LLVMdev] Proposal: ASan debugging API

[Kuba Břečka]

Hi,

I would like to improve the debugging experience for ASan. The idea is to
have a couple of useful commands in LLDB (probably implemented as Python
scripts) that could help the user when they are debugging an ASan-enabled
binary. We already have some debugging API (asan_interface.h):

    // Print the description of addr (useful when debugging in gdb).
    void __asan_describe_address(void *addr);

What I'd like to have is a few more API on the ASan/compiler-rt side to
query various information that ASan can provide, both about an error report
and about general addresses, something like:

    // Useful for calling from a debugger to get information about an error.
    // If an error has been (or is beign) reported, returns the pc, bp, sp,
    // address, access type, access type and bug description, and the return
    // value of the function is 1. If no error occurred yet, returns 0.
    int __asan_get_report_data(void **pc, void **bp, void **sp, void **addr,
                               int *is_write, size_t *access_size,
                               char **bug_description);

    // Address/memory type from ASan's point of view.
    typedef enum {
      __ADDRESS_TYPE_UNKNOWN,
      __ADDRESS_TYPE_SHADOW_LOW,
      __ADDRESS_TYPE_SHADOW_GAP,
      __ADDRESS_TYPE_SHADOW_HIGH,
      __ADDRESS_TYPE_GLOBAL,
      __ADDRESS_TYPE_STACK,
      __ADDRESS_TYPE_HEAP,
    } asan_address_type;

    // Useful for calling from the debugger to get information about a
pointer.
    // Return one of the __ADDRESS_TYPE_* enum values. If global or stack,
tries
    // to also return the variable name, address and size. If heap, tries to
    // return the chunk address and size.
    int __asan_get_address_type(void *addr, char **region_name,
                                void **region_address, size_t *region_size);

    // Useful for calling from the debugger to get the allocation stack
trace
    // and thread ID for a heap address. Returns 1 on success, 0 on error.
    int __asan_get_alloc_stack(void *addr, void **trace, size_t
*frame_count,
                               void **top_frame_bp, int *thread_id);

    // Useful for calling from the debugger to get the free stack trace
    // and thread ID for a heap address. Returns 1 on success, 0 on error.
    int __asan_get_free_stack(void *addr, void **trace, size_t *frame_count,
                              void **top_frame_bp, int *thread_id);

    // Useful for calling from the debugger to get the current shadow memory
    // mapping.
    void __asan_get_shadow_mapping(size_t *shadow_scale, size_t
*shadow_offset);
Hi,

I would like to improve the debugging experience for ASan. The idea is to
have a couple of useful commands in LLDB (probably implemented as Python
scripts) that could help the user when they are debugging an ASan-enabled
binary. We already have some debugging API (asan_interface.h):

    // Print the description of addr (useful when debugging in gdb).
    void __asan_describe_address(void *addr);

What I'd like to have is a few more API to query various information that
ASan can provide, both about an error report and about general addresses,
something like:

    // Useful for calling from a debugger to get information about an error.
    // If an error has been (or is being) reported, returns the pc, bp, sp,
    // address, access type, access type and bug description, and the return
    // value of the function is 1. If no error occurred yet, returns 0.
    int __asan_get_report_data(void **pc, void **bp, void **sp, void **addr,
                               int *is_write, size_t *access_size,
                               char **bug_description);

    // Address/memory type from ASan's point of view.
    typedef enum {
      __ADDRESS_TYPE_UNKNOWN,
      __ADDRESS_TYPE_SHADOW_LOW,
      __ADDRESS_TYPE_SHADOW_GAP,
      __ADDRESS_TYPE_SHADOW_HIGH,
      __ADDRESS_TYPE_GLOBAL,
      __ADDRESS_TYPE_STACK,
      __ADDRESS_TYPE_HEAP,
    } asan_address_type;

    // Useful for calling from the debugger to get information about a
pointer.
    // Return one of the __ADDRESS_TYPE_* enum values. If global or stack,
tries
    // to also return the variable name, address and size. If heap, tries to
    // return the chunk address and size.
    int __asan_get_address_type(void *addr, char **region_name,
                                void **region_address, size_t *region_size);

    // Useful for calling from the debugger to get the allocation stack
trace
    // and thread ID for a heap address. Returns 1 on success, 0 on error.
    int __asan_get_alloc_stack(void *addr, void **trace, size_t
*frame_count,
                               void **top_frame_bp, int *thread_id);

    // Useful for calling from the debugger to get the free stack trace
    // and thread ID for a heap address. Returns 1 on success, 0 on error.
    int __asan_get_free_stack(void *addr, void **trace, size_t *frame_count,
                              void **top_frame_bp, int *thread_id);

    // Useful for calling from the debugger to get the current shadow memory
    // mapping.
    void __asan_get_shadow_mapping(size_t *shadow_scale, size_t
*shadow_offset);

The information that this API would provide is currently only available in
the textual form in ASan reports. Having an API to provide it would enable
implementation of various tools/script for LLDB and GDB.

Kuba
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