Separate system call path from trap path. Passes usertests on 1 and 2 cpus.

defs.h

@@ -9,6 +9,7 @@ struct spinlock;
 struct sleeplock;
 struct stat;
 struct superblock;
+struct sysframe;
 
 // bio.c
 void            binit(void);
@@ -156,7 +157,7 @@ int             argaddr(int, uint64 *);
 int             fetchint(uint64, int*);
 int             fetchstr(uint64, char**);
 int             fetchaddr(uint64, uint64*);
-void            syscall(void);
+void            syscall(struct sysframe*);
 
 // timer.c
 void            timerinit(void);

exec.c

@@ -85,8 +85,8 @@ exec(char *path, char **argv)
   ustack[1] = argc;
   ustack[2] = sp - (argc+1)*sizeof(uint64);  // argv pointer
 
-  curproc->tf->rdi = argc;
-  curproc->tf->rsi = sp - (argc+1)*sizeof(uint64);
+  curproc->sf->rdi = argc;
+  curproc->sf->rsi = sp - (argc+1)*sizeof(uint64);
 
   sp -= (3+argc+1) * sizeof(uint64);
   if(copyout(pgdir, sp, ustack, (3+argc+1)*sizeof(uint64)) < 0)
@@ -102,9 +102,8 @@ exec(char *path, char **argv)
   oldpgdir = curproc->pgdir;
   curproc->pgdir = pgdir;
   curproc->sz = sz;
-  curproc->tf->rip = elf.entry;  // main
-  curproc->tf->rcx = elf.entry;
-  curproc->tf->rsp = sp;
+  curproc->sf->rcx = elf.entry;  // main
+  curproc->sf->rsp = sp;
   switchuvm(curproc);
   freevm(oldpgdir, oldsz);
   return 0;

proc.c

@@ -17,10 +17,8 @@ static struct proc *initproc;
 int nextpid = 1;
 extern void forkret(void);
 
-// we can return two ways out of the kernel and
-// for new processes we can choose either way
+// for returning  out of the kernel
 extern void sysexit(void);
-extern void trapret(void);
 
 static void wakeup1(void *chan);
 
@@ -102,16 +100,16 @@ found:
   }
   sp = p->kstack + KSTACKSIZE;
 
-  // Leave room for trap frame.
-  sp -= sizeof *p->tf;
+  // Leave room for syscall frame.
+  sp -= sizeof *p->sf;
 
   if ((uint64) sp % 16)
     panic("misaligned sp");
 
-  p->tf = (struct trapframe*)sp;
+  p->sf = (struct sysframe*)sp;
 
   // Set up new context to start executing at forkret,
-  // which returns to trapret.
+  // which returns to sysexit.
   sp -= sizeof(uint64);
   *(uint64*)sp = (uint64)sysexit;
 
@@ -138,12 +136,10 @@ userinit(void)
     panic("userinit: out of memory?");
   inituvm(p->pgdir, _binary_initcode_start, (uint64)_binary_initcode_size);
   p->sz = PGSIZE;
-  memset(p->tf, 0, sizeof(*p->tf));
-  p->tf->cs = SEG_UCODE | DPL_USER;
-  p->tf->ss = SEG_UDATA | DPL_USER;
-  p->tf->r11 = FL_IF;
-  p->tf->rsp = PGSIZE;
-  p->tf->rcx = 0;  // beginning of initcode.S
+  memset(p->sf, 0, sizeof(*p->sf));
+  p->sf->r11 = FL_IF;
+  p->sf->rsp = PGSIZE;
+  p->sf->rcx = 0;  // beginning of initcode.S
 
   safestrcpy(p->name, "initcode", sizeof(p->name));
   p->cwd = namei("/");
@@ -204,10 +200,10 @@ fork(void)
   }
   np->sz = curproc->sz;
   np->parent = curproc;
-  *np->tf = *curproc->tf;
+  *np->sf = *curproc->sf;
 
   // Clear %eax so that fork returns 0 in the child.
-  np->tf->rax = 0;
+  np->sf->rax = 0;
 
   for(i = 0; i < NOFILE; i++)
     if(curproc->ofile[i])

proc.h

@@ -47,7 +47,7 @@ struct proc {
   enum procstate state;        // Process state
   int pid;                     // Process ID
   struct proc *parent;         // Parent process
-  struct trapframe *tf;        // Trap frame for current syscall
+  struct sysframe *sf;         // Syscall frame for current syscall
   struct context *context;     // swtch() here to run process
   void *chan;                  // If non-zero, sleeping on chan
   int killed;                  // If non-zero, have been killed

syscall.c

@@ -62,17 +62,17 @@ fetcharg(int n)
   struct proc *curproc = myproc();
   switch (n) {
   case 0:
-    return curproc->tf->rdi;
+    return curproc->sf->rdi;
   case 1:
-    return curproc->tf->rsi;
+    return curproc->sf->rsi;
   case 2:
-    return curproc->tf->rdx;
+    return curproc->sf->rdx;
   case 3:
-    return curproc->tf->r10;
+    return curproc->sf->r10;
   case 4:
-    return curproc->tf->r8;
+    return curproc->sf->r8;
   case 5:
-    return curproc->tf->r9;
+    return curproc->sf->r9;
   }
   panic("fetcharg");
   return -1;
@@ -169,18 +169,31 @@ static int (*syscalls[])(void) = {
 [SYS_close]   sys_close,
 };
 
-void
-syscall(void)
+static void
+dosyscall(void)
 {
   int num;
   struct proc *curproc = myproc();
 
-  num = curproc->tf->rax;
+  num = curproc->sf->rax;
   if(num > 0 && num < NELEM(syscalls) && syscalls[num]) {
-    curproc->tf->rax = syscalls[num]();
+    curproc->sf->rax = syscalls[num]();
   } else {
     cprintf("%d %s: unknown sys call %d\n",
             curproc->pid, curproc->name, num);
-    curproc->tf->rax = -1;
+    curproc->sf->rax = -1;
   }
 }
+
+void
+syscall(struct sysframe *sf)
+{
+    if(myproc()->killed)
+      exit();
+    myproc()->sf = sf;
+    dosyscall();
+    if(myproc()->killed)
+      exit();
+    return;
+}
+

trap.c

@@ -41,16 +41,6 @@ idtinit(void)
 void
 trap(struct trapframe *tf)
 {
-  if(tf->trapno == T_SYSCALL){
-    if(myproc()->killed)
-      exit();
-    myproc()->tf = tf;
-    syscall();
-    if(myproc()->killed)
-      exit();
-    return;
-  }
-
   switch(tf->trapno){
   case T_IRQ0 + IRQ_TIMER:
     if(cpuid() == 0){

trapasm.S

@@ -25,7 +25,7 @@ alltraps:
   push %rbx
   push %rax
 
-  cmpw $KCSEG, CSOFF(%rsp)   # compare to saved cs
+  cmpw $SEG_KCODE, CSOFF(%rsp)   # compare to saved cs
   jz 1f 
   swapgs
   
@@ -36,7 +36,7 @@ alltraps:
 .globl trapret
 trapret:
   cli
-  cmpw $KCSEG, CSOFF(%rsp)  # compare to saved cs
+  cmpw $SEG_KCODE, CSOFF(%rsp)  # compare to saved cs
   jz 1f
   swapgs
 
@@ -58,11 +58,12 @@ trapret:
 
   add $16, %rsp  # discard trapnum and errorcode
   iretq
+
 #PAGEBREAK!
 
-# syscall_entry jumps here after syscall instruction
+# syscall jumps here after syscall instruction
 .globl sysentry
-sysentry:  # Build trap frame.
+sysentry:  # Build syscall frame.
   // load kernel stack address
   swapgs
   movq  %rax, %gs:0  // save %rax in syscallno of cpu entry
@@ -75,63 +76,54 @@ sysentry:  # Build trap frame.
   movq  %rax, %rsp
   movq  %gs:0, %rax  // restore rax
 
-  // push usp to make a valid trapframe
-  push $(UDSEG|0x3)
   push %gs:8
-  // safe eflags and eip
-  push %r11
-  push $(UCSEG|0x3)
   push %rcx
-  // push errno and trapno to make stack look like a trap
-  push $0
-  push $64
-
-  // push values on kernel stack
-  push %r15
-  push %r14
-  push %r13
-  push %r12
   push %r11	
-  push %r10
+  push %rax	
+
+  push %rbp
+  push %rbx	
+  push %r12 
+  push %r13
+  push %r14
+  push %r15	
+
   push %r9
   push %r8	
-  push %rdi
-  push %rsi
-  push %rbp
+  push %r10
   push %rdx
-  push %rcx
-  push %rbx
-  push %rax
+  push %rsi	
+  push %rdi
 	
   mov  %rsp, %rdi  # frame in arg1
 
-  call trap
-#PAGEBREAK!
+  call syscall
+  # fall through to sysexit
 	
-# Return falls through to trapret...
 .globl sysexit
 sysexit:
   # to make sure we don't get any interrupts on the user stack while in
   # supervisor mode.  insufficient?  (see vunerability reports for sysret)
   cli
 	
-  pop %rax
-  pop %rbx
-  pop %rcx
-  pop %rdx
-  pop %rbp
-  pop %rsi
   pop %rdi
+  pop %rsi
+  pop %rdx
+  pop %r10
   pop %r8
   pop %r9
-  pop %r10
-  pop %r11
-  pop %r12
-  pop %r13
-  pop %r14
-  pop %r15
 
-  add $(5*8), %rsp  # discard trapnum, errorcode, rip, cs and rflags
+  pop %r15
+  pop %r14
+  pop %r13
+  pop %r12
+  pop %rbx
+  pop %rbp
+
+  pop %rax
+  pop %r11
+  pop %rcx
+
   mov (%rsp),%rsp  # switch to the user stack
   # there are two more values on the stack, but we don't care about them	
   swapgs	

x86.h

@@ -166,6 +166,33 @@ struct trapframe {
    uint64 ss;      
 }__attribute__((packed));
 
+struct sysframe {
+  // arguments
+  uint64 rdi;
+  uint64 rsi;
+  uint64 rdx;
+  uint64 r10;
+  uint64 r8;
+  uint64 r9;
+  
+  // callee-saved registers
+  uint64 r15;
+  uint64 r14;
+  uint64 r13;
+  uint64 r12;
+  uint64 rbx;
+  uint64 rbp;
+
+  // return value
+  uint64 rax;
+
+  // syscall registers
+  uint64 r11;   // eflags
+  uint64 rcx;   // rip
+  uint64 rsp;
+  
+}__attribute__((packed));
+
 #endif
 
 #define TF_CS 144 // offset in trapframe for saved cs