From 0ac8fdc499d7261cae8bbfc1e7fb7b171bb8aceb Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Mon, 5 Jan 2026 14:20:39 -0800
Subject: [PATCH] wip - annotated disassembly

---
 hello/hello-fwrite.txt | 124 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 124 insertions(+)
 create mode 100644 hello/hello-fwrite.txt

diff --git a/hello/hello-fwrite.txt b/hello/hello-fwrite.txt
new file mode 100644
index 0000000..086ce97
--- /dev/null
+++ b/hello/hello-fwrite.txt
@@ -0,0 +1,124 @@
+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