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Spill registers before scanning the stack.
From the change: // xtensa has more registers than an instruction can address. The 16 that // can be addressed are called the "window". When a function is called or // returns the window rotates. This allows for more efficient function calls // because ram doesn't need to be used. It's only used if the window wraps // around onto itself. At that point values are "spilled" to empty spots in // the stack that were set aside. When the window rotates back around (on // function return), the values are restored into the register from ram. // So, in order to read the values in the stack scan we must make sure all // of the register values we care about have been spilled to RAM. Luckily, // there is a HAL call to do it. There is a bit of a race condition here // because the register value could change after it's been restored but that // is unlikely to happen with a heap pointer while we do a GC. Fixes adafruit#2907
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2 files changed

Lines changed: 42 additions & 1 deletion

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‎ports/esp32s2/mphalport.c‎

Lines changed: 19 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -37,6 +37,24 @@ void mp_hal_delay_us(mp_uint_t delay) {
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mp_hal_delay_ms(delay / 1000);
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}
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mp_uint_t cpu_get_regs_and_sp(mp_uint_t *regs) {
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// This is provided by the esp-idf/components/xtensa/esp32s2/libhal.a binary
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// blob.
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extern void xthal_window_spill(void);
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mp_uint_t cpu_get_regs_and_sp(mp_uint_t *regs, uint8_t reg_count) {
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// xtensa has more registers than an instruction can address. The 16 that
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// can be addressed are called the "window". When a function is called or
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// returns the window rotates. This allows for more efficient function calls
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// because ram doesn't need to be used. It's only used if the window wraps
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// around onto itself. At that point values are "spilled" to empty spots in
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// the stack that were set aside. When the window rotates back around (on
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// function return), the values are restored into the register from ram.
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// So, in order to read the values in the stack scan we must make sure all
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// of the register values we care about have been spilled to RAM. Luckily,
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// there is a HAL call to do it. There is a bit of a race condition here
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// because the register value could change after it's been restored but that
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// is unlikely to happen with a heap pointer while we do a GC.
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xthal_window_spill();
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return (mp_uint_t) __builtin_frame_address(0);
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}

‎ports/esp32s2/tools/decode_backtrace.py‎

Lines changed: 23 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,23 @@
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"""Simple script that translates "Backtrace:" lines from the ESP output to files
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and line numbers.
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Run with: python3 tools/decode_backtrace.py <board>
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Enter the backtrace line at the "? " prompt. CTRL-C to exit the script.
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"""
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import subprocess
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import sys
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board = sys.argv[1]
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print(board)
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while True:
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addresses = input("? ")
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if addresses.startswith("Backtrace:"):
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addresses = addresses[len("Backtrace:"):]
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addresses = addresses.strip().split()
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addresses = [address.split(":")[0] for address in addresses]
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print('got', addresses)
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subprocess.run(["xtensa-esp32s2-elf-addr2line",
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"-e", "build-{}/firmware.elf".format(board)] + addresses)

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