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wip - annotated disassembly

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Brooke Vibber 2026-01-05 14:20:39 -08:00
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0000000000010b36 <fwrite>:
; ra = return address
; a0 = buffer
; a1 = size
; a2 = count
; a3 = stream
; -- Entry point for fwrite
; Function protocol
10b36: 7139 addi sp,sp,-64
; Check an internal word in the FILE to see if it needs to lock
10b38: 08c6a783 lw a5,140(a3)
10b3c: f426 sd s1,40(sp)
; Set s1 = 1 if a1/size is non-zezro
10b3e: 00b034b3 snez s1,a1
10b42: f822 sd s0,48(sp)
10b44: f04a sd s2,32(sp)
10b46: ec4e sd s3,24(sp)
; Set s1 = -1 if a1/size is non-zero
10b48: 409004b3 neg s1,s1
10b4c: fc06 sd ra,56(sp)
10b4e: e852 sd s4,16(sp)
; Set s0 = size * count
10b50: 02c58433 mul s0,a1,a2
; Set s2 = stream
10b54: 8936 mv s2,a3
; Set s3 = size
10b56: 89ae mv s3,a1
; Set s1 = count if size is non-zero, or 0 if size is zero
10b58: 8cf1 and s1,s1,a2
; Branch to lock path if needed:
10b5a: 0207d463 bgez a5,10b82 <fwrite+0x4c>
; -- exit point bgez: likely branch 10b5e, rare branch 10b82
; -- entry through branch
; Call through to __fwritex
10b5e: 8636 mv a2,a3
10b60: 85a2 mv a1,s0
10b62: f27ff0ef jal 10a88 <__fwritex>
; -- exit point jal, return address 10b66
; -- Entry point from return
; Check the return value from __fwritex to see if we wrote
; all requested bytes.
10b66: 8a2a mv s4,a0
10b68: 01440463 beq s0,s4,10b70 <fwrite+0x3a>
; -- exit point beq: likely 10b6c, rare 10b70
; -- Entry point from 10ba6
; -- Entry point from 10baa
; Note this overlaps the previous trace!
; Check the return value from __fwritex to see if we wrote
; all requested bytes.
10b68: 01440463 beq s0,s4,10b70 <fwrite+0x3a>
; -- exit point beq: likely 10b6c, rare 10b70
; -- Entry point from 10b68
; Divide to the count in records from the count in bytes
10b6c: 033a54b3 divu s1,s4,s3
; Function outro
10b70: 70e2 ld ra,56(sp)
10b72: 7442 ld s0,48(sp)
10b74: 7902 ld s2,32(sp)
10b76: 69e2 ld s3,24(sp)
10b78: 6a42 ld s4,16(sp)
10b7a: 8526 mv a0,s1
10b7c: 74a2 ld s1,40(sp)
10b7e: 6121 addi sp,sp,64
10b80: 8082 ret
; -- end point ret
; Entry point from 10b68
; Return the original record count, skipping the division.
; Note this overlaps the previous two traces!
10b70: 70e2 ld ra,56(sp)
10b72: 7442 ld s0,48(sp)
10b74: 7902 ld s2,32(sp)
10b76: 69e2 ld s3,24(sp)
10b78: 6a42 ld s4,16(sp)
10b7a: 8526 mv a0,s1
10b7c: 74a2 ld s1,40(sp)
10b7e: 6121 addi sp,sp,64
10b80: 8082 ret
; -- end point ret
; Lock the FILE if needed
; Call through to __lockfile
10b82: 8a2a mv s4,a0
10b84: 8536 mv a0,a3
10b86: e456 sd s5,8(sp)
10b88: c95ff0ef jal 1081c <__lockfile>
; -- end point jal - return address 10b8c
; -- entry through return address
; Call through to __fwritex
10b8c: 8aaa mv s5,a0
10b8e: 864a mv a2,s2
10b90: 8552 mv a0,s4
10b92: 85a2 mv a1,s0
10b94: ef5ff0ef jal 10a88 <__fwritex>
; -- exit through call; return address 10b98
; -- entry through return address
10b98: 8a2a mv s4,a0
10b9a: 000a8763 beqz s5,10ba8 <fwrite+0x72>
; -- exit through beqz; likely branch 10b9e; rare branch 10ba8
; -- entry through branch from 10b9a
; Call through to __unlockfile
10b9e: 854a mv a0,s2
10ba0: d25ff0ef jal 108c4 <__unlockfile>
; -- end through jal; return address 10ba4
; -- entry through return address
10ba4: 6aa2 ld s5,8(sp)
10ba6: b7c9 j 10b68 <fwrite+0x32>
; -- exit through jump to 10b68
; -- entry point from branch at 10b9a
; Head back to the exit path
10ba8: 6aa2 ld s5,8(sp)
10baa: bf7d j 10b68 <fwrite+0x32>
; -- exit through jump to 10b68