Abolish PSPSym from ABI

docs/design/coreclr/botr/clr-abi.md

@@ -322,33 +322,9 @@ Finally1:
 
 Note that JIT64 does not implement this properly. The C# compiler used to always insert all necessary "step" blocks. The Roslyn C# compiler at one point did not, but then was changed to once again insert them.
 
-## The PSPSym and funclet parameters
+## Funclet parameters
 
-The *PSPSym* (which stands for Previous Stack Pointer Symbol) is a pointer-sized local variable used to access locals from the main function body.
-
-NativeAOT does not use PSPSym. For filter funclets the VM sets the frame register to be the same as the parent function. For second pass funclets the VM restores all non-volatile registers. The same convention is used across all platforms.
-
-CoreCLR uses PSPSym for all platforms except x86: the frame pointer on x86 is always preserved when the handlers are invoked.
-
-First, two definitions.
-
-*Caller-SP* is the value of the stack pointer in a function's caller before the call instruction is executed. That is, when function A calls function B, Caller-SP for B is the value of the stack pointer immediately before the call instruction in A (calling B) was executed. Note that this definition holds for both AMD64, which pushes the return value when a call instruction is executed, and for ARM, which doesn't. For AMD64, Caller-SP is the address above the call return address.
-
-*Initial-SP* is the initial value of the stack pointer after the fixed-size portion of the frame has been allocated. That is, before any "alloca"-type allocations.
-
-The value stored in PSPSym is the value of Initial-SP for AMD64 or Caller-SP for other platforms, for the main function. The stack offset of the PSPSym is reported to the VM in the GC information header. The value reported in the GC information is the offset of the PSPSym from Initial-SP for AMD64 or Caller-SP for other platforms. (Note that both the value stored, and the way the value is reported to the VM, differs between architectures. In particular, note that most things in the GC information header are reported as offsets relative to Caller-SP, but PSPSym on AMD64 is one exception, and maybe the only exception.)
-
-The VM uses the PSPSym to find other locals it cares about (such as the generics context in a funclet frame). The JIT uses it to re-establish the frame pointer register, so that the frame pointer is the same value in a funclet as it is in the main function body.
-
-When a funclet is called, it is passed the *Establisher Frame Pointer*. For AMD64 this is true for all funclets and it is passed as the first argument in RCX, but for ARM and ARM64 this is only true for first pass funclets (currently just filters) and it is passed as the second argument in R1. The Establisher Frame Pointer is a stack pointer of an interesting "parent" frame in the exception processing system. For the CLR, it points either to the main function frame or a dynamically enclosing funclet frame from the same function, for the funclet being invoked. The value of the Establisher Frame Pointer is Initial-SP on AMD64, Caller-SP on x86, ARM, and ARM64.
-
-Using the establisher frame, the funclet wants to load the value of the PSPSym. Since we don't know if the Establisher Frame is from the main function or a funclet, we design the main function and funclet frame layouts to place the PSPSym at an identical, small, constant offset from the Establisher Frame in each case. (This is also required because we only report a single offset to the PSPSym in the GC information, and that offset must be valid for the main function and all of its funclets). Then, the funclet uses this known offset to compute the PSPSym address and read its value. From this, it can compute the value of the frame pointer (which is a constant offset from the PSPSym value) and set the frame register to be the same as the parent function. Also, the funclet writes the value of the PSPSym to its own frame's PSPSym. This "copying" of the PSPSym happens for every funclet invocation, in particular, for every nested funclet invocation.
-
-On ARM and ARM64, for all second pass funclets (finally, fault, catch, and filter-handler) the VM restores all non-volatile registers to their values within the parent frame. This includes the frame register (`R11`). Thus, the PSPSym is not used to recompute the frame pointer register in this case, though the PSPSym is copied to the funclet's frame, as for all funclets.
-
-Catch, Filter, and Filter-handlers also get an Exception object (GC ref) as an argument (`REG_EXCEPTION_OBJECT`). On AMD64 it is the second argument and thus passed in RDX. On ARM and ARM64 this is the first argument and passed in R0.
-
-(Note that the JIT64 source code contains a comment that says, "The current CLR doesn't always pass the correct establisher frame to the funclet. Funclet may receive establisher frame of funclet when expecting that of original routine." It indicates this is the reason that a PSPSym is required in all funclets as well as the main function, whereas if the establisher frame was correctly reported, the PSPSym could be omitted in some cases.)
+Catch, Filter, and Filter-handlers get an Exception object (GC ref) as an argument (`REG_EXCEPTION_OBJECT`). On AMD64 it is passed in RCX (Windows ABI) or RSI (Unix ABI). On ARM and ARM64 this is the first argument and passed in R0.
 
 ## Funclet Return Values
 
@@ -374,11 +350,11 @@ Some definitions:
 
 When an exception occurs, the VM is invoked to do some processing. If the exception is within a "try" region, it eventually calls a corresponding handler (which also includes calling filters). The exception location within a function might be where a "throw" instruction executes, the point of a processor exception like null pointer dereference or divide by zero, or the point of a call where the callee threw an exception but did not catch it.
 
-On AMD64, all register values that existed at the exception point in the corresponding "try" region are trashed on entry to the funclet. That is, the only registers that have known values are those of the funclet parameters.
+The VM sets the frame register to be the same as the parent function. This allows the funclets to access local variables using frame-relative addresses.
 
-On ARM and ARM64, all registers are restored to their values at the exception point.
+On CoreCLR/AMD64, all other register values that existed at the exception point in the corresponding "try" region are trashed on entry to the funclet. That is, the only registers that have known values are those of the funclet parameters and the frame register.
 
-On x86: TBD.
+On all other platforms and NativeAOT/AMD64, all non-volatile registers are restored to their values at the exception point.
 
 ### Registers on return from a funclet
 
@@ -696,12 +672,6 @@ x64 currently saves RBP, RSI and RDI while ARM64 saves just FP and LR.
 
 However, EnC remap is not supported inside funclets. The stack layout of funclets does not matter for EnC.
 
-## Considerations with regards to PSPSym
-
-As explained previously in this document, on x64 we have Initial RSP == PSPSym. For EnC methods, as we disallow remappings after localloc (see below), we furthermore have RBP == PSPSym.
-For ARM64 we have Caller SP == PSPSym and the FP points to the previously saved FP/LR pair. For EnC the JIT always sets up the stack frame so that the FP/LR pair is at Caller SP - 16 and does not save any additional callee saves.
-These invariants allow the VM to compute new value of the frame pointer and PSPSym after the edit without any additional information. Note that the frame pointer and PSPSym do not change values or location on ARM64. However, EH may be added to a function in which case a new PSPSym needs to be materialized, even on ARM64. Location of PSPSym is found via GC info.
-
 ## Localloc
 
 Localloc is allowed in EnC code, but remap is disallowed after the method has executed a localloc instruction. VM uses the invariants above (`RSP == RBP` on x64, `FP + 16 == SP + stack size` on ARM64) to detect whether localloc was executed by the method.

docs/design/coreclr/botr/guide-for-porting.md

@@ -386,12 +386,10 @@ Here is an annotated list of the stubs implemented for Unix on Arm64.
         application
 
     11. `CallEHFunclet` – Used to call catch, finally and fault funclets. Behavior
-        is specific to exactly how funclets are implemented. Only used if
-        USE_FUNCLET_CALL_HELPER is set
+        is specific to exactly how funclets are implemented.
 
     12. `CallEHFilterFunclet` – Used to call filter funclets. Behavior is specific
-        to exactly how funclets are implemented. Only used if
-        USE_FUNCLET_CALL_HELPER is set
+        to exactly how funclets are implemented.
 
     13. `ResolveWorkerChainLookupAsmStub`/ `ResolveWorkerAsmStub` Used for virtual
         stub dispatch (virtual call support for interface, and some virtual

docs/design/features/OsrDetailsAndDebugging.md

@@ -307,8 +307,6 @@ On Arm64 we have epilog unwind codes and the second SP adjust does not appear to
 
 OSR funclets are more or less normal funclets.
 
-On Arm64, to satisfy PSPSym reporting constraints, the funclet frame must be padded to include the Tier0 frame size. This is conceptually similar to the way the funclet frames also pad for homed varargs arguments -- in both cases the padded space is never used, it is just there to ensure the PSPSym ends up at the same caller-SP relative offset for the main function and any funclet.
-
 #### OSR Unwind Info
 
 On x64 the prolog unwind includes a phantom SP adjustment at offset 0 for the Tier0 frame.

src/coreclr/gcinfo/gcinfoencoder.cpp

@@ -357,7 +357,6 @@ GcInfoSize& GcInfoSize::operator+=(const GcInfoSize& other)
     SecObjSize += other.SecObjSize;
     GsCookieSize += other.GsCookieSize;
     GenericsCtxSize += other.GenericsCtxSize;
-    PspSymSize += other.PspSymSize;
     StackBaseSize += other.StackBaseSize;
     ReversePInvokeFrameSize += other.ReversePInvokeFrameSize;
     FixedAreaSize += other.FixedAreaSize;
@@ -406,7 +405,6 @@ void GcInfoSize::Log(DWORD level, const char * header)
         LogSpew(LF_GCINFO, level, "Prolog/Epilog: %zu\n", ProEpilogSize);
         LogSpew(LF_GCINFO, level, "SecObj: %zu\n", SecObjSize);
         LogSpew(LF_GCINFO, level, "GsCookie: %zu\n", GsCookieSize);
-        LogSpew(LF_GCINFO, level, "PspSym: %zu\n", PspSymSize);
         LogSpew(LF_GCINFO, level, "GenericsCtx: %zu\n", GenericsCtxSize);
         LogSpew(LF_GCINFO, level, "StackBase: %zu\n", StackBaseSize);
         LogSpew(LF_GCINFO, level, "FixedArea: %zu\n", FixedAreaSize);
@@ -471,7 +469,6 @@ template <typename GcInfoEncoding> TGcInfoEncoder<GcInfoEncoding>::TGcInfoEncode
     m_GSCookieValidRangeStart = 0;
     _ASSERTE(sizeof(m_GSCookieValidRangeEnd) == sizeof(UINT32));
     m_GSCookieValidRangeEnd = (UINT32) (-1); // == UINT32.MaxValue
-    m_PSPSymStackSlot = NO_PSP_SYM;
     m_GenericsInstContextStackSlot = NO_GENERICS_INST_CONTEXT;
     m_contextParamType = GENERIC_CONTEXTPARAM_NONE;
 
@@ -702,14 +699,6 @@ template <typename GcInfoEncoding> void TGcInfoEncoder<GcInfoEncoding>::SetGSCoo
     m_GSCookieValidRangeEnd   = validRangeEnd;
 }
 
-template <typename GcInfoEncoding> void TGcInfoEncoder<GcInfoEncoding>::SetPSPSymStackSlot( INT32 spOffsetPSPSym )
-{
-    _ASSERTE( spOffsetPSPSym != NO_PSP_SYM );
-    _ASSERTE( m_PSPSymStackSlot == NO_PSP_SYM || m_PSPSymStackSlot == spOffsetPSPSym );
-
-    m_PSPSymStackSlot              = spOffsetPSPSym;
-}
-
 template <typename GcInfoEncoding> void TGcInfoEncoder<GcInfoEncoding>::SetGenericsInstContextStackSlot( INT32 spOffsetGenericsContext, GENERIC_CONTEXTPARAM_TYPE type)
 {
     _ASSERTE( spOffsetGenericsContext != NO_GENERICS_INST_CONTEXT);
@@ -941,7 +930,7 @@ template <typename GcInfoEncoding> void TGcInfoEncoder<GcInfoEncoding>::Build()
     UINT32 hasContextParamType = (m_GenericsInstContextStackSlot != NO_GENERICS_INST_CONTEXT);
     UINT32 hasReversePInvokeFrame = (m_ReversePInvokeFrameSlot != NO_REVERSE_PINVOKE_FRAME);
 
-    BOOL slimHeader = (!m_IsVarArg && !hasGSCookie && (m_PSPSymStackSlot == NO_PSP_SYM) &&
+    BOOL slimHeader = (!m_IsVarArg && !hasGSCookie &&
         !hasContextParamType && (m_InterruptibleRanges.Count() == 0) && !hasReversePInvokeFrame &&
         ((m_StackBaseRegister == NO_STACK_BASE_REGISTER) || (GcInfoEncoding::NORMALIZE_STACK_BASE_REGISTER(m_StackBaseRegister) == 0))) &&
 #ifdef TARGET_AMD64
@@ -970,7 +959,7 @@ template <typename GcInfoEncoding> void TGcInfoEncoder<GcInfoEncoding>::Build()
         GCINFO_WRITE(m_Info1, (m_IsVarArg ? 1 : 0), 1, FlagsSize);
         GCINFO_WRITE(m_Info1, 0 /* unused - was hasSecurityObject */, 1, FlagsSize);
         GCINFO_WRITE(m_Info1, (hasGSCookie ? 1 : 0), 1, FlagsSize);
-        GCINFO_WRITE(m_Info1, ((m_PSPSymStackSlot != NO_PSP_SYM) ? 1 : 0), 1, FlagsSize);
+        GCINFO_WRITE(m_Info1, 0 /* unused - was hasPSPSymStackSlot */, 1, FlagsSize);
         GCINFO_WRITE(m_Info1, m_contextParamType, 2, FlagsSize);
 #if defined(TARGET_LOONGARCH64)
         assert(m_StackBaseRegister == 22 || 3 == m_StackBaseRegister);
@@ -1037,17 +1026,6 @@ template <typename GcInfoEncoding> void TGcInfoEncoder<GcInfoEncoding>::Build()
 
     }
 
-    // Encode the offset to the PSPSym.
-    // The PSPSym is relative to the caller SP on IA64 and the initial stack pointer before stack allocations on X64.
-    if(m_PSPSymStackSlot != NO_PSP_SYM)
-    {
-        _ASSERTE(!slimHeader);
-#ifdef _DEBUG
-        LOG((LF_GCINFO, LL_INFO1000, "Parent PSP at " FMT_STK "\n", DBG_STK(m_PSPSymStackSlot)));
-#endif
-        GCINFO_WRITE_VARL_S(m_Info1, GcInfoEncoding::NORMALIZE_STACK_SLOT(m_PSPSymStackSlot), GcInfoEncoding::PSP_SYM_STACK_SLOT_ENCBASE, PspSymSize);
-    }
-
     // Encode the offset to the generics type context.
     if(m_GenericsInstContextStackSlot != NO_GENERICS_INST_CONTEXT)
     {

src/coreclr/inc/eetwain.h

@@ -483,10 +483,10 @@ PTR_VOID GetExactGenericsToken(PREGDISPLAY     pContext,
                                EECodeInfo *    pCodeInfo);
 
 static
-PTR_VOID GetExactGenericsToken(SIZE_T          baseStackSlot,
+PTR_VOID GetExactGenericsToken(TADDR           sp,
+                               TADDR           fp,
                                EECodeInfo *    pCodeInfo);
 
-
 #endif // FEATURE_EH_FUNCLETS && USE_GC_INFO_DECODER
 
 /*

src/coreclr/inc/gcinfodecoder.h

@@ -583,6 +583,7 @@ class TGcInfoDecoder
     INT32   GetReversePInvokeFrameStackSlot();
     bool    HasMethodDescGenericsInstContext();
     bool    HasMethodTableGenericsInstContext();
+    bool    HasStackBaseRegister();
     bool    GetIsVarArg();
     bool    WantsReportOnlyLeaf();
 #if defined(TARGET_ARM) || defined(TARGET_ARM64) || defined(TARGET_LOONGARCH64) || defined(TARGET_RISCV64)

src/coreclr/inc/gcinfoencoder.h

@@ -23,7 +23,7 @@
     - Flag:     isVarArg,
                 unused (was hasSecurityObject),
                 hasGSCookie,
-                hasPSPSymStackSlot,
+                unused (was hasPSPSymStackSlot),
                 hasGenericsInstContextStackSlot,
                 hasStackBaseregister,
                 wantsReportOnlyLeaf (AMD64 use only),
@@ -34,9 +34,9 @@
     - CodeLength
     - Prolog (if hasGenericsInstContextStackSlot || hasGSCookie)
     - Epilog (if hasGSCookie)
-    - SecurityObjectStackSlot (if any)
+    - SecurityObjectStackSlot (if any; no longer used)
     - GSCookieStackSlot (if any)
-    - PSPSymStackSlot (if any)
+    - PSPSymStackSlot (if any; no longer used)
     - GenericsInstContextStackSlot (if any)
     - StackBaseRegister (if any)
     - SizeOfEditAndContinuePreservedArea (if any)
@@ -128,7 +128,6 @@ struct GcInfoSize
     size_t ProEpilogSize;
     size_t SecObjSize;
     size_t GsCookieSize;
-    size_t PspSymSize;
     size_t GenericsCtxSize;
     size_t StackBaseSize;
     size_t ReversePInvokeFrameSize;
@@ -408,7 +407,6 @@ class TGcInfoEncoder
 
     void SetPrologSize( UINT32 prologSize );
     void SetGSCookieStackSlot( INT32 spOffsetGSCookie, UINT32 validRangeStart, UINT32 validRangeEnd );
-    void SetPSPSymStackSlot( INT32 spOffsetPSPSym );
     void SetGenericsInstContextStackSlot( INT32 spOffsetGenericsContext, GENERIC_CONTEXTPARAM_TYPE type);
     void SetReversePInvokeFrameSlot(INT32 spOffset);
     void SetIsVarArg();
@@ -492,7 +490,6 @@ class TGcInfoEncoder
     INT32  m_GSCookieStackSlot;
     UINT32 m_GSCookieValidRangeStart;
     UINT32 m_GSCookieValidRangeEnd;
-    INT32  m_PSPSymStackSlot;
     INT32  m_GenericsInstContextStackSlot;
     GENERIC_CONTEXTPARAM_TYPE m_contextParamType;
     UINT32 m_CodeLength;