Search for: All records

Abstract The research on gradual typing has led to many variations on the Gradually Typed Lambda Calculus (GTLC) of Siek & Taha (2006) and its underlying cast calculus. For example, Wadler and Findler (2009) added blame tracking, Siek et al . (2009) investigated alternate cast evaluation strategies, and Herman et al . (2010) replaced casts with coercions for space efficiency. The meta-theory for the GTLC has also expanded beyond type safety to include blame safety (Tobin-Hochstadt & Felleisen, 2006), space consumption (Herman et al ., 2010), and the gradual guarantees (Siek et al ., 2015). These results have been proven for some variations of the GTLC but not others. Furthermore, researchers continue to develop variations on the GTLC, but establishing all of the meta-theory for new variations is time-consuming. This article identifies abstractions that capture similarities between many cast calculi in the form of two parameterized cast calculi, one for the purposes of language specification and the other to guide space-efficient implementations. The article then develops reusable meta-theory for these two calculi, proving type safety, blame safety, the gradual guarantees, and space consumption. Finally, the article instantiates this meta-theory for eight cast calculi including five from the literature and three new calculi. All of these definitions and theorems, including the two parameterized calculi, the reusable meta-theory, and the eight instantiations, are mechanized in Agda making extensive use of module parameters and dependent records to define the abstractions. 

In this paper, we present HYPERRACE, an LLVM-based tool for instrumenting SGX enclave programs to eradicate all side-channel threats due to Hyper-Threading. HYPERRACE creates a shadow thread for each enclave thread and asks the underlying untrusted operating system to schedule both threads on the same physical core whenever enclave code is invoked, so that Hyper-Threading side channels are closed completely. Without placing additional trust in the operating system’s CPU scheduler, HYPERRACE conducts a physical-core co-location test: it first constructs a communication channel between the threads using a shared variable inside the enclave and then measures the communication speed to verify that the communication indeed takes place in the shared L1 data cache—a strong indicator of physical-core co-location. The key novelty of the work is the measurement of communication speed without a trustworthy clock; instead, relative time measurements are taken via contrived data races on the shared variable. It is worth noting that the emphasis of HYPERRACE’s defense against Hyper-Threading side channels is because they are open research problems. In fact, HYPERRACE also detects the occurrence of exception- or interrupt-based side channels, the solutions of which have been studied by several prior works. 

The Antarctic Cold Reversal (ACR; 14.7 to 13 thousand years ago; ka) phase of the last deglaciation saw a pause in the rise of atmospheric CO₂and Antarctic temperature, that contrasted with warming in the North. A reexpansion of sea ice and a northward shift in the position of the westerly winds in the Southern Ocean are well‐documented, but the response of deep‐sea biota and the primary drivers of habitat viability remain unclear. Here, we present a new perspective on ecological changes in the deglacial Southern Ocean, including multifaunal benthic assemblage (foraminifera and cold‐water corals) and coral geochemical data (Ba/Ca and δ¹¹B) from the Drake Passage. Our records show that, during the ACR, peak abundances of thick‐walled benthic foraminiferaUvigerina bifurcataand corals are observed at shallow depths in the sub‐Antarctic (∼300 m), while coral populations at greater depths and further south diminished. Our ecological and geochemical data indicate that habitat shifts were dictated by (a) a northward migration of food supply (primary production) into the sub‐Antarctic Zone and (b) poorly oxygenated seawater at depth during this Antarctic cooling interval.